I may need to swap out the motherboard and if I do it will be a newer
model with the 775 socket. I will use a model 640 3.2 GHz Intel. The big
concern I have is that the Ethernet will be a different make and model.
What do I need to do in order to deal with that?

I have swapped the same model of motherboards out but not different
models. I have the Asus P4C800-E with the Intel 478 3.2 GHz CPU and I'm
looking either an Asus P5LD2 or Asus P5B. The P5B is in a backup server
in storage. Could I just take the hard drive out and put it in a
different PC with the P5B motherboard. It has the same model Adaptec
Scsi Board.

The problem I'm having is noise on our Brooktrout Faxserver board. I'm
going to try a new Power Supply first and then the motherboard is the
only thing left. I have a spare Brooktrout and swapped it out but the
noise was still there.