Windows Remote Desktop will turf you off the PC that's being accessed from outside.
I use "LogMeIn" free, and that does allow it. In fact, someone can sit at the accessed PC and see stuff happening.
I used to use a VPN to access my home PC when away, but MS removed Remote Desktop from the Home User edition of Win 7. I tried various VNC packages: some worked fairly well, some didn't. But LogMeIn is so easy that I only use the VPN now to transfer files from the home PC to the laptop or vice-versa.
I think there was an earlier MS utility that allowed "remote assistance" and "teaching" over the net, but it's too long ago and I don't remember the name of the package.