Fujixerox in Australia sells a C1110b color printer with USB, not a printer available here in the USA.
On the XP box, you have the printer marked as shared and the Guest account on, right?
On Vista I add printer, then choose the find printer not in list, and click a browse button to the right. Click on the XP PC. In the end you get something like \\xppc\printer
None of this is special to Xerox, a Windows forum may be more helpful.
I tried to remain child-like, all I acheived was childish.