I don't know a lot about it from the PC side but you should be able to use VNC (Virtual Network Computing) to do this. In your case you need a VNC server on the Mac and a VNC client on the PC. I don't have any links but a Google search will turn up plenty of info.
I do this but in reverse; WinVNC server on Windows PCs and 'Chicken of the VNC' client on the Mac (strange name, great app 🙂).