If you only want single desktop access, by which I mean one computer, one remote desktop user at a time, then I use RealVNC. I find it works pretty well and the pricing isn't exhorbitant.
I also have a Mini OS 10.6 Server, on which runs Aqua Connect, which allows multiple remote desktop users (much like Windows Server). I like both RealVNC and AC, but find that for part-time personnel, who require remote access only to their computers from home for e-mail, Filemaker etc., RealVNC does the trick.
For my own access to desktops I also use Timbuktu, but would not recommend this as a solution to virtualization.
Hope that's of some use,