iPhones timing out when sync

Hello. I got a new iPhone & have tried to Sync it but it keeps timing out in iTunes. I updated iTunes to the latest & have now updated the iPhone to 1.1.3. This stopped working, so i restarted the computer as iTunes got stuck then restored the phone which did the update to. The iPhone synced fine this morning after the restore & update but every time I sync now it tells me either it can't find the phone or that it timed out. I had a unlocked 1.1.1 version before & this did the same. I have plugged my unlocked iPhone into my daughters computer & it synced & everything fine. I am doing something wrong or just missing something. Any advice would be great.

I have a iMac 20", 2GHz, Intel Core 2 Duo, 250gb, Leopard Mac OS X v10.5 etc.

Thanks for your time.