Did you a perform a repair on your Windows installation. The OS already installed was probably configured for your old motherboard and windows won't automatically pick up settings for your new one. So try inserting your XP installation CD and selecting Repair, when it asks for it.
I have an odd problem with my computer. I installed a new motherboard with no issues, but now when I start up the computer it continually asks me if I want to boot in safe mode, safe mode with networking, safe with command, last known good configuration or normally. It doesnt matter what I pick, the computer will reboot and go to the exact same thing everytime. Ive disconnected cd-rom and tried, same thing. Not sure what is causing this. Any help is appreciated.