Stupid question

I have a desktop running Windows 2000, and I'll be getting a new laptop at work which is running XP.

How can I create a workgroup in Windows 2000 that I can then join XP into? I want to be able to transfer my disk images from the laptop to my desktop for safe keeping. And since we run a lot of apps that could wreak havoc with my Operating System I want to keep a fresh backup within reach. I was thinking a mapped network drive to a folder on the Desktop would be the best way to go.

Along those same lines, what difficulty is there in networking the two PC VIA USB 2.0? USB 2.0 is heaps faster than 100Mmps Ethernet that I have right now.