Concurrent remote desktop in windows with multiple session support

I'd like to have a remote desktop solution that allows me to connect to remote PCs even while other users are logged in, using a different session. The whole idea is that the user working locally in the remote system can work normally without being disturbed by the remote user.

I have tried TightVNC but I couldn't figure out how to enter into an independent session.

I have also read about a hack for Windows XP (also for Windows 7) but I'd let it as a last resort solution since it's rather nasty.

You can't do this as standard with the desktop operating systems as they are specifically configured to be single user systems. You can do it with the server versions of Windows but that's a bit drastic (and expensive for home use). As you say, there are hacks about to give multiuser functionality, but these do have licence implications, and there used to be some boards and apps that allowed multi-user operation but I haven't come across any recently.

The hack is your only option unless you have a server version of windows there is no easy way to do it.