To mpeg4

Actually i have bought this archos gmini4 , kinda mp3 playuer which has an LCD screen to where in u can watch movies etc .....but i have a problem...it says u can just see mpeg4 format movies. and it has a software where in u can convert avi to mpeg4 . but not other formats . i just wanted to know is there any way to convert .DAT, .mov etc to avi or mpeg4..

Thankx