Movies on an R4?

Can you put movies on an R4 to play on a DS and if so, what format do they need to be in?

yes, you can, and they need to be in .dpg format.

Use SUPER or BatchDPG to convert movies into NDS Mpeg, a format used by moonshell. Or you can use TunaXvids which uses .avi at extremely low quality. Unsure if it works.