I never managed to get Remote Desktop Client working myself, but I have successfully vnced my XP Pro pc with my Mac OS X (Panther) and the other way around. All with the use of free software.
On the PC:
TightVNC - only thing you'll need. The download contains a server and client software.
On Mac:
Client -
VNCThing I've tried a few mac clients and this was by far the best and easiest.
Server -
OSXvnc Extremely simple to set up and, most importantly, it works.
With some port forwarding and little effort you should be able to use your mac on your pc or vice versa

SSH is faster and more powerful than VNC but you basically have no visual interface. It simply lets you use the command line/terminal on the machines. I personally don't know all the fancy code you have to use in Terminal, so I stuck with VNC.