iPhone wont finish restoring

My dad's iPhone 3GS is on 3.1.2 and he asked me to update his to 3.1.3 today.
I plugged it into my MacBook pro. Launched iTunes and click update.
Evereything went well until the very end. The last bit of the update bar won't move. I waited for like half and hour, but it still wouldn't move. I tried restoring it and the same problem occur.
How can i update his phone, he need by tomorrow.

Thanks

ok....
I tried pluging it into my iMac and it works with one try.
I'm assuming that the problem is with my iTunes. What could be the problem?