Windows equivalent to a Linux product?

[Steve]

Ok so the question usually goes.
"What can I use in Linux to replace Windows only program (x)"
I need to reverse the question.
Someone wants me to teach them a thing or three about about windows,
and I'm glad to oblige them.  However I need to find a VNC equivalent
for XP.  Unless there is something in windows, that I can access via
Linux, that I can use to accomplish this.
Any ideas?