Run Marvins and select the second option (create a patcher package?) - let it search your entire install disk (might as well...)
Once it's done, it'll put a folder on your desktop
Personally, I open the folder, find and copy "patcher" and "cpuid.txt" to my "root drive" (your "working" drive - the one you installed OSX to...)
Restart
(you need to boot into "single user mode")
Press a key to stop the countdown
type -s and hit Enter (to start single user mode)
(it'll display lines of text and eventually stop at a "command prompt")
type the following: ( hit Enter at the end of each line )

mount -uw /
./patcher ./cpuid.txt
(lots of text saying what it's done)
reboot (restarts the computer)
-or-
exit (quits single user mode and resumes booting into the OS (right?))

the computer will restart.

(if you didn't move those 2 files out of the folder, you'll have to change the directory TO the folder before the "./patcher" command...)

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Running both 10.5.8 and 10.6.4 on my stinking AMD/ATi machine...