As promised I've put together a (rather hasty) walkthrough detailing how to:
* Network your OS-X / XP machines up
* Setup file sharing
* Install and configure VNC software enabling you to control your PC from your Mac
It's kind of lengthy - I had no idea how many steps there are until you break it down! I've tried to make it straightforward for people who have never played around with networking before, but I may have missed stuff out so *please* shout if anything doesn't make sense or is obviously missing.
The tutorial is in basic text form from my website:
I hope people find this useful!