Hi, well video drivers will have a say in DVD performance. Are you using the official drivers or a beta version? my experience with ATI is there beta drivers are well deserved to be called "beta". I have used beta radeon drivers that caused lock up during dvd playback. If you do not have the "official" drivers give them a try.
Pentium 3 1000 @ 1100 ( windows 2000 server), Abit bx-133, 256 Mb Mushkin Rev.3 cas 2-2-2, ATI Radeon
AMD Thunderbird 1.4 @ 1.63 (24/7) IWILL KK266R , Corsairs pc 150 cl2, Leadtek GeForce 3