FFmpeg might work - I will give it a try tomorrow:
ffmpeg -i [your_video.wmv] -r 20 -ar 44100 -ab 196 -b 300k -aspect 4:3 -s 320x240 -croptop 0 -cropbottom 0 -cropleft 0 -cropright 0 [your_video.mp4]
-r 20 is the framerate [frames/second]
-ar 44100 is the audio rate [samples/second]
-ab 196 is audio 196 kbit/s
-b 300k is the video bitrate of 300 kbit/s
-aspect 4:3 is the desired aspect ratio
-s 320x240 will scale to E8 screen resolution
The WMVs have a resolution of 640x480.
Thanks for the replies - I'll try them all!