Sure, a PC DVD-ROM will play DVD movies fine. If you haven't bought a DVDROM yet, make sure you get one that can be made regionless though...
A hardware decoder would let you play DVDs even on, say, a P150. However a lot of video cards have hardware motion compensation which is kind of like partial hardware DVD acceleration. With that, a 500MHz CPU (like mine!) should offer perfect playback, assuming you get proper support in the DVD player.