Buy an R4. The ds alone is not capable of playing movies. If you buy an R4, add a memory card (I use a sandisk 8gig) and upload the movies into the memory card, you can go to the moonshell menu in the R4 and play the movies from there. Unfortunately, it is very difficult to find an R4 these days as some people were using it to illegally download and play games for free.
Jesus
April 2010