Yes but don't have to convert them to mp4. If you install buzzplayer, you can download (or copy through iTunes) and read any video file format with buzz player, inc divx.
The oher great thing with buzz player is that you don't necessary need to have the video file physically present on the iPad: you also can stream the videos from your pc or from a server....
IMO if you intend to use your iPad to watch videos, buzz player is a must-have (and I've tested many video/divx players out there).