Possible fix for OS X Leopard. (at your own risk!)

Follow these steps to recover from the blue screen of death!

1. Reboot into single-user mode (hold Cmd-S while booting machine)
2. Follow the directions OSX gives you when you get to the prompt (I think these were them - just type the two commands it tells you to):
fsck -fy /
/sbin/mount -uw /
3. Remove the following files:
rm -rf /Library/Preference Panes/Application Enhancer.prefpane
rm -rf /Library/Frameworks/Application Enhancer.framework
rm -rf /System/Library/SystemConfiguration/Application Enhancer.bundle
rm -rf /Library/Preferences/com.unsanity.ape.plist
4. Exit, to continue booting normally
exit

Might help - has helped many up to know.