Motherboard Swap On System

My main XP Pro machine failed last night, with symptomology consistent with an actual failure of the motherboard. I'm going to try and attack it methodically tonight, but realistically I think the board will be "pining for the fjords.".I would like to take the primary disk from that machine, and cable it into the
old backup desktop machine in place of that machine's primary hard drive while I figure out what to do. That way I won't have to spend major amounts of time getting the Outlook .pst file moved and configured, not to mention all the other relatively important stuff sitting on that main machine.When I've done that in the past, that has always required a reinstall of Windows because the motherboards are totally different architectures and obviously take a different set of drivers and dlls and what have you.But I have a hunch this is not necessary if one knows the right tricks or perhaps how to run the mysterious Repair console.

Can anyone talk me through what I need to do in order to stick a hard drive with a good, running XP Pro installation onto a foreign machine? A second question: I run a small network at home cable modem into SMC .Barricade 4 port hub. The failing machine connects to the hub, as does a wireless router. I've found that when my primary machine is turned off (or in the case of this failure, is dead) that none of my networking works wired or wireless. I had to cable the backup desktop machine directly into the cable modem in order to have any connectivity. Just wired into the hub it waits forever for an IP address. I just don't understand what the main machine has to do with the networking process thought that was the job of the hub.