I have a 2.16 Ghz, Macbook Pro. I recently downloaded the Mac Combo Update and installed it. at about 90% the screen went blue with the little loading circle in the lower center.
I restarted it and it shows a error message + a message in dark block to restart by pressing the Power button.
Ooh... that's a kernel panic (hard system crash, that is) at startup. Not a good sign--means something went seriously wrong with the installation of the update, which screwed up your OSX install.
There may be easier ways to fix this, but as far as I know the best bet is to start up from the DVD that came with the computer and do an "archive and install" reinstall of everything. This should preserve your data and user information, but get a clean, working copy of the OS installed.
Then reinstall the update and hope it goes better.