what does it say on the screen?
I tried to update before and it was a black screen with something like:
I think you have to have it NOT set to 1.50 hombrew kernel.
If it says the above, and is still on a text screen, with NOT the official update, pull the battery out, go to recovery, and check your hombrew kernel settings. That's what I had to do when I made the mistake,of having it set to 1.50 kernel.