Apple's new version of their Remote Desktop software totes the ability to control Mac's, Windows, and Linux.
http://www.apple.com/remotedesktop/
Every time I turn around, the lines that seperate the OS's seem to become more and more blurred. Not thats its a bad thing, but considering how long its taken to start getting that way, ouch. Wasnt too long ago when *nix, Win and Mac's couldnt talk to anything but their own.
And damn if its not cheap. It practically does everything MS SMS can do and its only 500 bucks for Unlimited clients.
Also, there is a front end for RDC called RDC Menu. It allows better control over multiple sessions. I have taken the liberty of uploading it here. It is NOT a ZIP file so just rename it back to .dmg and you're all set.
Thanks,
Wilnix