I hope I'm not misunderstanding you, but there's a reasonably well-known Mac and Windows remote-control package called Timbuktu. It runs on OS's at least as far as back as 8.x, and probably before that. I just bought the OS X upgrade, and it continues to work very well. I couldn't live without it.
You can get it from Netopia. They've got some kind of time-limited, full-featured trial version you can use without purchasing.