[bluedeer]

I've found this converter which I've used to batch convert videos from whatever format they were in to Windows Media Player Mobile-friendly files. So far, everything I've thrown at it has converted and played! You may have to tweak settings, but I recommend setting it for Mp4 and Medium. May be a good idea to ensure your videos are properly converted and padded appropriately for a 640x480 file so when you convert it, the image will be exactly 320x240.

The program is pretty self-explanatory.

Enjoy!