How do I get Windows Media PLayer to Stretch Videos?

Ok I have been using betaplayer exclusively with my pda as it plays all the formats I need except now I have setup a way to stream TV from my PC to my PPC so I can watch my cable channels wherever I am thanks to beyond TV. The caveat is it streams using wmv/asf format and betaplayer does not support this streaming format. So I am using Media pLayer trying to stream a 320X240 video on my 640X480 VGA pc and the video is centered and is letterboxed in the center and isnt using up all the pixels even in full screen mode. How the hell do I get it to play like betaplayer which streches videos to use all the pixels? I mean since 320X240 are multiples of 640X480 all it needs to do is pixel double, how come it doesnt do this?