Its a good thing I'm a linux guru then.
Ok, here is the solution to my own question
Start up a second vncserver, with the desired resolution (say, 800x600) and connect to that. Vnc viewers will default to being in a window, with an option to fullscreen.
Sadly, I beleve this will only work in linux where you can have multiple desktop screens ;( I was hoping for a more elegent solution but.. oh well! ;D