Proving once again that new doesn't always mean better, I did a fresh reinstall of Leopard 10.5.4, reinstalled Logic 8.0, and this time, instead of using the latest Vienna Instruments and Syncrosoft LCC files, used the versions on the CD included with my VSL SE: everything loads perfectly now.
I'm going to use Time Machine from now on and backup after every software update to make sure I can recover from software updates breaking my installs.
Thanks for everyone's help!
If I could just figure out this line break thing. I'm writing this on Firefox and it's still not formatting correctly :P