Gallery, the built in app, plays MP4 videos. Convert using the free version of Any Video Converter.
Video Converter, DVD Ripper - Any Video converter - The versatile video converter for iPod, iPhone, PSP, Zune, cell phones and more
Then mount the Droid using a USB cable, create a folder at root level called vids. Copy the MP4 file there.
Unmount the Droid. Open Gallery.
At least that's what works for me.