Well, I'm going to go with you have a 4GB Hard Drive. So after you mod it, you will have maybe 3GB free space. For playing DVD's, I'd suggest Donglefree DVD Player. And then for the emulators, get emulators! I haven't checked the files section for awhile, so I don't know if the files are there.
Ok, in the file section I see some programs you should get. DVD2Xbox is a great program to have, I strongly recommend it. Get the 7.7 version if the 7.8 version gives you trouble. Then there is linksbox if you want to surf the web on your Xbox. surf the files section and see what there is for ya
I also know that Zzk2001 has a nice CD you can burn and use on your Xbox that has tons of emulators, trainers, programs, everything.