After years, years of avoiding serious Windows use I'm finally having to wrestle with two Microsoft products. Windows 2000 and Virtual PC. Although the "Virtual Switch" mode of VPC is specifically intended to allow you to log into the windows box as a separate entity from the host Mac OS X box, this only kinda sorta works. I can log into VPC from a different computer -- the iMac in the other room for example. No problem. But I can't log in from the same machine (the host). So for now my workaround is to create a circular connection where I mount the windows drive on my iMac and then mount that on my powerbook.
I'm also running cygwin in Windows and logging into that. Layers.