Sotz, If the player you bought is the
***NEW***Rhodium - 2 inch TFT LCD MP4 Player w/ Speaker 256MB - Black(Support SD card) then according to the specs:
:100% BRAND NEW High Quality MP3 / MP4 / PMP AMV Player
:Support WMV, MPG, MPEG I, MEG II, and AVI Convert to AMV playing (Software included) So it only supports AMV format video which means you have to convert all your video to this format. With a 2.0 inch screen it should support a resolution of 208x176 at 10fps but you will find they will run smother if you convert them to 208x144 at 12fps.
You will need MP3 Player Utilities 4.05 to get the AMV converter for these sizes, you can download it
HERE