If your PC is behind a firewall, or has the Windows firewall running, you will need to poke a hole in it to allow a remote-control application to access it. In any case, I use RealVNC which is free, and allows remote access/control to/from Windows and Linux (and Solaris) systems. I use it both directions. There are a number of interoperable implementations. Some folks prefer other versions than RealVNC.

Another option is logmein.com. If your primarily worried about windows boxes, you can install the log me in agent and then remote in from the website.

No firewall holes. No VPN. It's a simple management console and works very well. So so sure it if works for linux yet.

I use it and it works well for my windows box... then I ssh or vnc to my linux box.

*I don't work for them... it's just a nice tool.

VNC sounds like the best option for you, its free, pretty easy to setup. As woboyle says, you'll need to check the firewall issue but there are quite a few guides on opening ports on a firewall.

If you're connecting to Windows machines then using RDP is another option, works very much like VNC and there are clients for Linux which allow you to connect to Windows (tsclient for example).