Remote Display must be installed on both the PC and the PPC, you must be ActiveSynced and have cerdisp running on both devices.
I usually get connected with ASync, then start cerdisp on my PC and then start it on the PPC.
It is not FAST, by any means, but if you can pause your game on the PPC, the PC Image should match within a couple of seconds, then try the screen cap on the PC.
Barring anything else, you could always take the Neandertal approach and take an actual picture of the screen and then "clean it up" in a photoshop type program on your PC.
