cortilla,
It would help knowing your motherboard's details. Without it, I cannot tell you which drivers you need to load for it. nVidia, VIA, SiS, and ATI all have specific drivers for their motherboard chipsets and if the motherboard comes with onboard video, there are specific drivers for it too.
All this could affect DVD Playback as well as the performance of your computer. (Especially is the DVD Player is in PIO Mode do to the lack of proper IDE Drivers.)
If you have region locked DVD Software, that could be the problem, if the DVDs you are attempting to play are not from that particular region.
Which model is your DVD Player? (There could be a Firmware update for your player that will handle some of the new copy protections used on the DVD Media.)
Take Care,
Richard