ripped dvds are a complicated. there are multiple ways to rip them. (note, i am assuming that you own the original dvd, because if you dont then you shouldnt read any of teh following instructions because that would be illegal, GASP!)
the easiest way to rip a dvd is to make an image of the disc using dvd decrypter. (
http://www.dvddecrypter.com/) this will create an image on your hard drive of the ENTIRE disc, extras features, obscure language tracks, special features, subtitles, etc. this can total up to 8.5 GB (on a dual layer dvd) to play this, you need to mount this disc image on a virtual drive, using a program like alcohol 120% (discontinued, tear) or daemon tools. then, using media center, you can just go to discs and drives and watch teh disc image as if it were in your hard drive.
now, because 8.5 GB is a lot of space, you can easily compress this. the best program that i know of is auto gordian knot (
http://www.autogk.net/web/). this will either take the original physical dvd or an image ripped by dvd decrypter and convert it to AVI, using XviD to compress it. you can leave watever sound you want, (dolby digital AC3, or just stereo etc.) and even add subtitles. set it to run, and a few hours later (as long as you have an intel processor, an AMD will take longer (although some people say XviD encodes faster on AMDs, they claim the codec is designed specifically for the athlon 64, but i digress)) its all done. you can watch it in media center like a regular avi.
hope this solves your problems, have any questions about the specific programs here, reply, i dunno how much you know about dvd ripping, encoding, etc. have a nice day!