VNC is an open source remote desktop protocol. microsoft uses the proprietary RDC. IMO VNC is better and thats what Leopard uses to screen share.
to connect to my PC at home from my Mac and vice versa i have screen sharing enabled on my Mac in sharing preferences and a password set in the settings. then on the PC i installed TightVNC and unblocked from the windows firewall which is all pretty automatic when setting up Tight VNC.
then on the Mac you can either open the Screen Sharing app which is in /System/Library/CoreServices and type in yout PC's IP address or press "command-K" in the Finder and type "vnc://your PC's IP address" in the server address field.
on the PC leave TightVNC server open and the open the viewer and type in your Mac's IP address.
