Hi there !
there are several ways...
One get a 'double' license for Timbuktu, that's probably the best way I use it myself !
You could turn on 'Remote Login' in the Mac's network preferences...then get a good SSH client such as 'Putty' for XP and then you can login in to the Mac via SSH and do anything you want...this is all done via the command line though...
Alternatively, every Mac (OSX Tiger) has a built in VNC server...
So if you turn on 'Apple Remote Desktop' in the System Preferrnces then make sure that 'VNC viewers may view screen with password' is checked...this will allow you to operate your Mac from a PC....
I'll add a better tutorial/screenshots later...
regards
Ric