I don't know if this will answer your question or not, but...
XP Pro's Remote Desktop (Connection) does not handle VNC connections -- it only establishes a connection using the RDP (MS-centric) protocol. Seeing as how Apple's Remote Desktop server app utilizes VNC, as well as there being free VNC implementations available for Mac OS X (aka OSXVnc), you're going to need a VNC program on your PC.
Essentially you run the VNC server on your Macintosh -- if you have Apple's remote desktop, I've had issues connecting standard VNC clients to it -- and then use a VNC client on your PC. For a PC VNC client, I use
UltraVNC. Assuming you have all the proper ports (usually 5900 to 5910) forwarded in your home firewall, you can point your UltraVNC session to your Macintosh's IP address and you should be able to connect.
If your workplace employs a firewall that blocks outgoing connections, you may have to implement
tunneling, which is something I'll let you look into and research on your own time. I'd recommend this method anyway, though, as it's a more secure way of VNCing.
Of course, you can also try the
Timbuktu Pro over Skype method. Problem with this is that you have to pay for Timbuktu Pro, and it requires two application installs rather than the one VNC client.