we networked a xp and a vista at work. it did not work. we were told by microsoft that it would not network. when we networked them things on the xp would just dissappear. i kept accusing my secretary of deleting things. microsoft said there were many problems networking the two. that was about 1 year ago
Microsoft addressed this interoperability issue with the LLTD client shortly after Vista was released. See my post above if you're still having issues getting Vista and XP to work together. I use Vista Business Ultimate at home, my wife's and kids computers are XP. We all see each others shared drives and printers just fine with the LLTD client installed on the XP machines.
I share files all the time between XP and Vista. Vista’s security is a lot tighter than XP’s. I just set up the shares and looked for the box in Network.