Can't install Security Updates [so no Safari...]

Question

Hello...
I'm having myriad issues with my admittedly old computer, but this one is driving me nuts. I can download the application and mount it, but then get the HD icon with a red exclamation mark, and the message:
"This volume is not supported", or something like that. I have tried several security updates, all of which should supposedly work with my operating system.
Any ideas??
Many thanks.

Answer 1

I have a boilerplate response which I'll post below. Are you using the correct security update version (PPC vs. Intel)?
Updating
Certain steps appear to minimize the risk of an update producing problems.
Number one is to make sure you have a clone backup of your computer in case you do need to back out of it again. This is the only guaranteed way of not having to worry about the results of an update.
Some like to boot from their installer discs or an external backup and verify (and if necessary repair) their internal drives as well as drive permissions. This is done with Disk Utility. You can verify a drive while booted from the same drive but sometimes this produces spurious errors. Repairing a drive (if necessary) has to be done while booted from another disk. Permissions repair can, and is probably best, done when booted from your internal drive.
[Resolve startup issues and perform disk maintenance with Disk Utility and fsck|http://docs.info.apple.com/article.html?artnum=106214]
[Using Disk Utility in Mac OS X 10.4.3 or later|http://docs.info.apple.com/article.html?artnum=302672]
[Disk Utility's Repair Disk Permissions|http://docs.info.apple.com/article.html?artnum=25751]
You can also go to the step of booting into safe mode to do the install.
[Mac OS X: Starting up in Safe Mode|http://docs.info.apple.com/article.html?artnum=107393]
[What is Safe Boot, Safe Mode? (Mac OS X)|http://docs.info.apple.com/article.html?artnum=107392]
[Safe Boot takes longer than normal startup|http://docs.info.apple.com/article.html?artnum=107394]
I like to download the update onto my computer and install it from there rather than let Software Update do it. I know a few people who had problems with doing the update via software updater found a manual install to work.
Repair permissions again afterward.
It helps to only install one update at a time and to run the computer for a while to make sure it is behaving well.
The more cautious even like to unplug third party peripherals (see [comment by BDaqua|http://discussions.apple.com/message.jspa?messageID=9040746#9040746]).
Almost all of the above steps (except backup) have been questioned as to necessity because probably many people have done successful updates without doing them. I say they can't hurt, they can very likely do good (especially if your computer isn't regularly maintained), so why not do them to be safe.
[BDaqua's comments on updating problems|http://discussions.apple.com/message.jspa?messageID=8948595#8948595]
[Baby Boomer's comments on updating problems|http://discussions.apple.com/message.jspa?messageID=9025760#9025760]
[Security Update 2009-005 (Tiger PPC)|http://support.apple.com/downloads/DL931/en_US/SecUpd2009-005PPC.dmg]
[Security Update 2009-005 (Tiger Intel)|http://support.apple.com/downloads/DL932/en_US/SecUpd2009-005Intel.dmg]
This security update incorporates features in earlier updates.
[Apple Downloads web site|http://support.apple.com/downloads>
Currently no security update past 2009-005 has been released for Tiger (and may never be).