Thought others might be struggling with this one too:
After upgrading to Tiger, iCal consistently crashed on launch immediately after opening its main window. Trashing all preferences and associated calendars didn't relieve it. I tried a Archive and reinstall, no help. During this, searches of my main tips and troubleshooting sites didn't show others having this issue.
Then i finally discovered one webpage pointing to BurnoutMenu, a program I had long since moved on from.
Trash the /Library/SIMBL/Plugins/BurnoutMenuEnabler.bundle file, and iCal will spring to life under Tiger.
Hope this helps,
cms7912