I did try getting a USB-Parallel adaptor for my laser printer. The XP saw the printer and configured it, but print jobs fail to go to the printer. Perhaps the printer doesn't like both the parallel and USB ports connected at the same time.
My cheap B&W Lexmark laser at home is using both the Parallel (PC) and USB interfaces (Mac). Both work fine. I haven't tried a USB->Parallel adapter - I'd honestly be surprised if that worked reliably since the interfaces are so different.
How about a USB to Ethernet adapter for your printer? Something like this: http://www.provantag...-100~7QMS900L.htm (There may be cheaper things out there.)
I can't help on the networking stuff. I haven't ever tried to run 2 different subnets simultaneously. I assume you've seen things like this - http://www.uregina.c...535/cctn535.shtml
Good luck.
Cheers,
Scott.