The thread YouTube on Windows Mobile explains how to play YouTube (and Google, MetaCafe) on the PPC.
First install the TCPMP Player on the PPC. It’s a cab file that will need to be copied on the PPC and then start the installer from the PPC. Then unzip the Flash TCPMP Plugin and put the two plg files in the same directory where TCPMP got installed. Then on the PC, install iTube (I also installed the Google and Metacafe handlers). Then use iTube to grab the Youtube/Metacafe/Google videos and copy them to the PPC.