Movies (90-100 min long) vary from 200 MB to 300 MB when converted on default/better quality to .dpg..
About the games..The bigest game you can find at the time is 256 MB big (but there are only few, and JAP only!!), usually game size is from 32 MB - 128 MB..
If you use 2 GB card, and you want to fill it up, you can fit 20 games at least (but that's just if all games have 128 MB), take in consideration that you'll probably have some media on (music, movies, pictures, eBooks), and that all your ROMs will be trimmed, you can fit one or two movies, one or two music albums, bunch of pictures, few eBooks and up to 20-30 average games with no problem!!