is this what you tried? HKEY_Local_Machine > System > CurrentControlSet > and delete the ENUM key
if that's definitely NOT working, you can try this:
you can go into device manager and remove everything under "system devices" (that's all the stuff related to your mobo. Then shut down, install the new mobo and case, and boot up...WinXP will find all your new hardware and after a couple reboots you'll be set