I need to have both Snow leopard and Lion...Mountain lion running on my iMac. How do I install Lion or Mountain lion on an Ext H D and boot from it?

Question

   My software is obsolete (and now dead) in 10.7 so I need to keep Snow leopard alive to run that- but now things like TurboTax are dropping support for 10.6 or lower and I have to have lion or Mountain Lion available.  I actually downloaded Lion onto a thumb drive but never installed it when I found out that it would immedaitely render all my FreeHand files inaccessible (years of work!),  Now that I am forced to have an OS above 10.6 I was hoping I could install whichever--Lion or Mountain Lion onto an external hard drive and figure  out how to boot from that (found  something in archives I think, but I need words of one syllable or less).  This way I could, ideally, boot from either the External hard drive in the higher OS when needed, or from the internal hard drive when I need to use Snow leopard.  There is a long story here, but I think this is the gist.  I wasn not sure if this should be asked here or in either Lion or Mountain Lion (both of which I have, essentially, ignored since I would not be moving up until I could figure out how to access those old files of forms and drawings00but now I have no choice.  I am panicking now that I HAVE to make the move anbd cannot afford to buy another  Mac just to keep two separately running.  Any help would be greatly appreciated.  i asked Apple when Lion came out and they said there was no way to partition (even if I KNEW how to do that) the haaard drive and install both on my iMac-- but I "think" this is a bit different and possible???   Thanks  (once/if I figure this out, I need to figure out how to back-up but that is another matter)

Answer 1

You need to move to Windows 7, because Apple is now releasing a new OS X version annually and it's playing havoc with people's hardware and software.
Windows 7 will get support until 2020, that's 8 years of software stability, however you do need to make System Restore disks, boot disk and another on a hard drive to self restore (like TimeMachine is for OS X)
Apple has no plans to change their currrent behavior as all they care about is selling new hardware with a shiny new OS X verison on it.
If you wait to move, what will happen is you'll lose that full 8 years and will have to swtich to a newer Windows sooner
Windows 7 machines are still widely avaialble, despite Windows 8 (a failure) being pushed currently.
Running three OS X operating systems on one machine is quite a chore reserved for only seasoned computer geeks, then it's only going to last X months as the next OS X version will be released, then the next a year after that.
Another method would be to get a virtual machine software (virtualbox is free) and install Windows 7 into that to ease your transitition if you cant' spring for a Windows 7 machine, preferablly a tower that will last a long time.
Here is a method to run Snow Leopard in Parallels, however it's a unapproced hack and not for the comptuer newbie.
http://forums.macrumors.com/showthread.php?t=1365439
We have no control over Apple's OS X release cycle, nor the third party developers who make their own decisions what to support.
Our only choice as users to stop using both products and seek software/hardware stability.