Urgent 2003 SP1 problem

I just loaded SP1 update onto my 2003 Server DC. Install ran smoothly, and rebooted.
Machine is now stuck at "The Active Directory is rebuilding indices. Please wait..."
It has been like this for a couple of hours - any idea whether it's stuck in the loop forever, or should I be more patient and give it a few more hours.
Any more advice would be helpful.
Thanks
Si.