Handbrake is a really useful piece of free software I've been using recently. It enables you to convert and even edit DVDs so that you can play them on other devices. This includes a range of mobile devices like i-pod and Sony PSP as well as just playing them on your computer / TV.
It also gives you the option of copying them with the subtitles showing or just saving particular scenes and reduces the file sizes for storing back ups of your DVDs.
It's really useful and runs on a range of platforms MAC and Linux as well as Windows.
Hope you find it useful, but remember to respect copyright laws.