"blue screen" appears on startup after installation of Leopard?
Well, you probably had a certain application enhancer installed, that's to blame.
If you by some reason don't like this blue screen, try this:
Restard your computer into single-user mode by holding down
command () and the S-button (thats command-s)
When you're in the single-user mode type these commands, exactly as below:
(after each line hit return)
/sbin/fsck -fy
/sbin/mount -uw /
rm -rf /System/Library/SystemConfiguration/ApplicationEnhancer.bundle
reboot
If the problem persists, try something else... maybe reinstalling Leopard,
OR
try getting used to that blue screen...