What software do I need to play MPEG4 videos on my Axim x 50v?

The movies are recorded on my Audiovox DC400 Digital Video cvamera. I would like to just take the SD memory out of the camera and watch it on my Pocket PC

You might try TCPMP
http://tcpmp.corecodec.org/download

Or, check to see if there are any updates for Windows Media Player for your device.