Can I resize the screen resolution of a remote desktop session?

Add the following line to the RDP file (open with notepad):

smart sizing:i:1

About your only hope is to DISCONNECT the session (leaving it running by closing the RDP session without logging out), and then reconnect using a different resolution. Of course this will all depend on the server remote session settings, etc. This works in 2003/2008. No idea if it will work in 2000. The screen scaling in the VMWare client (and the old McAfeee RDesktop32) was very nice.

mstsc.exe /v server.dns.local /w 800 /h 600

Or something like that, will do it for you. Not really "on the fly" though.