Consequences of installing G5 Leopard on Intel Mac?

Question

I bought an Intel iMac off of eBay, and it came shipped with OS X 10.4. I had a non-retail replacement DVD of 10.5 from when I had an AppleCare problem with my iMac G5, so I tried to use that disc to upgrade my OS. It never worked correctly, and on the Apple forums I was told that the replacement DVD would be hardware-specific and not function.
However, a new phenomenon has occurred.. If I completely install Tiger with the hardware-specific discs that came with my intel Mac, and then simply upgrade to Leopard- the install succeeds and the computer is ESSENTIALLY functional.
It's not perfect though. What I've observed is that (today was the 2nd time this has happened) after a couple days of untinterrupted use (including powering down/up) and having a seemingly functional iMac-- everything goes very wrong. The computer slows down to a crawl, so I leave it alone; then when the beachball goes away, I try to click something. No matter what App I choose, it will freeze up once it begins, and everything I click suddenly stops working.
So do you think this is a consequence of installing a leopard disc with G5 architecture, or that these symptoms are indicative of something wrong with the iMac itself (possibly bad RAM?). What seems strange is the install does succeed with the upgrade, and the computer works great for a good while- and then suddenly stops. One thing that always confuses/annoys me is when computers aren't consistent... I mean, theyre computers!
Please share your thoughts, thank you!

Answer 1

In short: A PPC Mac cannot boot an Intel version of OS X and vice-versa. You will need a full retail version of Leopard that can install either the PPC or the Intel version of OS X. Or as you have discovered your Upgrade disc will install an Intel upgrade to an Intel version of Tiger or a PPC upgrade to a PPC version of Tiger, but it will not performa a full Erase and Install.
As for migrating from a G5 to an Intel Mac see the following:
A Basic Guide for Migrating to Intel-Macs
If you are migrating a PowerPC system (G3, G4, or G5) to an Intel-Mac be careful what you migrate. Keep in mind that some items that may get transferred will not work on Intel machines and may end up causing your computer's operating system to malfunction.
Rosetta supports "software that runs on the PowerPC G3, G4, or G5 processor that are built for Mac OS X". This excludes the items that are not universal binaries or simply will not work in Rosetta:
Classic Environment, and subsequently any Mac OS 9 or earlier applications
Screensavers written for the PowerPC
System Preference add-ons
All Unsanity Haxies
Browser and other plug-ins
Contextual Menu Items
Applications which specifically require the PowerPC G5
Kernel extensions
Java applications with JNI (PowerPC) libraries
See also What Can Be Translated by Rosetta.
In addition to the above you could also have problems with migrated cache files and/or cache files containing code that is incompatible.
If you migrate a user folder that contains any of these items, you may find that your Intel-Mac is malfunctioning. It would be wise to take care when migrating your systems from a PowerPC platform to an Intel-Mac platform to assure that you do not migrate these incompatible items.
If you have problems with applications not working, then completely uninstall said application and reinstall it from scratch. Take great care with Java applications and Java-based Peer-to-Peer applications. Many Java apps will not work on Intel-Macs as they are currently compiled. As of this time Limewire, Cabos, and Acquisition are available as universal binaries. Do not install browser plug-ins such as Flash or Shockwave from downloaded installers unless they are universal binaries. The version of OS X installed on your Intel-Mac comes with special compatible versions of Flash and Shockwave plug-ins for use with your browser.
The same problem will exist for any hardware drivers such as mouse software unless the drivers have been compiled as universal binaries. For third-party mice the current choices are USB Overdrive or SteerMouse. Contact the developer or manufacturer of your third-party mouse software to find out when a universal binary version will be available.
Also be careful with some backup utilities and third-party disk repair utilities. Disk Warrior 4.1, TechTool Pro 4.6.1, SuperDuper 2.5, and Drive Genius 2.0.2 work properly on Intel-Macs with Leopard. The same caution may apply to the many "maintenance" utilities that have not yet been converted to universal binaries. Leopard Cache Cleaner, Onyx, TinkerTool System, and Cocktail are now compatible with Leopard.
Before migrating or installing software on your Intel-Mac check MacFixit's Rosetta Compatibility Index.
Additional links that will be helpful to new Intel-Mac users:
Intel In Macs
Apple Guide to Universal Applications
MacInTouch List of Compatible Universal Binaries
MacInTouch List of Rosetta Compatible Applications
MacUpdate List of Intel-Compatible Software
Transferring data with Setup Assistant - Migration Assistant FAQ
Because Migration Assistant isn't the ideal way to migrate from PowerPC to Intel Macs, using Target Disk Mode, copying the critical contents to CD and DVD, an external hard drive, or networking
will work better when moving from PowerPC to Intel Macs. The initial section below discusses Target Disk Mode. It is then followed by a section which discusses networking with Macs that lack Firewire.
If both computers support the use of Firewire then you can use the following instructions:
1. Repair the hard drive and permissions using Disk Utility.
2. Backup your data. This is vitally important in case you make a mistake or there's some other problem.
3. Connect a Firewire cable between your old Mac and your new Intel Mac.
4. Startup your old Mac in Target Disk Mode.
5. Startup your new Mac for the first time, go through the setup and registration screens, but do NOT migrate data over. Get to your desktop on the new Mac without migrating any new data over.
If you are not able to use a Firewire connection (for example you have a Late 2008 MacBook that only supports USB:)
1. Set up a local home network: Creating a small Ethernet Network.
2. If you have a MacBook Air or Late 2008 MacBook see the following:
MacBook (13-inch, Aluminum, Late 2008) and MacBook Pro (15-inch, Late 2008)- Migration Tips and Tricks;
MacBook (13-inch, Aluminum, Late 2008) and MacBook Pro (15-inch, Late 2008)- What to do if migration is unsuccessful;
MacBook Air- Migration Tips and Tricks;
MacBook Air- Remote Disc, Migration, or Remote Install Mac OS X and wireless 802.11n networks.
Copy the following items from your old Mac to the new Mac:
In your /Home/ folder: Documents, Movies, Music, Pictures, and Sites folders.
In your /Home/Library/ folder:
/Home/Library/Application Support/AddressBook (copy the whole folder)
/Home/Library/Application Support/iCal (copy the whole folder)
Also in /Home/Library/Application Support (copy whatever else you need including folders for any third-party applications)
/Home/Library/Keychains (copy the whole folder)
/Home/Library/Mail (copy the whole folder)
/Home/Library/Preferences/ (copy the whole folder)
/Home /Library/Calendars (copy the whole folder)
/Home /Library/iTunes (copy the whole folder)
/Home /Library/Safari (copy the whole folder)
If you want cookies:
/Home/Library/Cookies/Cookies.plist
/Home/Library/Application Support/WebFoundation/HTTPCookies.plist
For Entourage users:
Entourage is in /Home/Documents/Microsoft User Data
Also in /Home/Library/Preferences/Microsoft
Credit goes to Macjack for this information.
If you need to transfer data for other applications please ask the vendor or ask in the Discussions where specific applications store their data.
5. Once you have transferred what you need restart the new Mac and test to make sure the contents are there for each of the applications.
Written by Kappy with additional contributions from a brody.
Revised 1/6/2009