Newer flash cards that fit into Slot 1 on the DS don't require you to flash your DS in order to use their card. All DS's and DS lites are flashable, there are just more complicated methods to doing this. In my honest opinion Flashing your DS is only good if you want to get rid of the Nintendo start up logo's.
Only the video file format .DPG will work - period. it also has to be in the right aspect ratio's to fit the DS's screen otherwise Moonshell will give you an error message. You will also have to make sure you have a few other files on your PC. You can even add subtitle files to your .dpg videos if your original video files had them.
Can't find the original link to Batch DPG but the latest version is the non-beta'd one, batchdpg v1.0.
A tutorial showing you how to use Batch DPG - http://au.youtube.com/watch?v=1fSFW4tkeAY