I'll start off by saying my machine used to play dvd's just fine. It's a P4 Northwood running at 3.2Ghz with a GeForce 6200. I'm running Slackware 10.1 with 2.6.13 from kernel.org. Yesterday, when I came home with my brand new copy of Alien I noticed the playback seemed jerky and it sucked up 100% cpu and dropped frames whenever I tried skipping ahead or back on the dvd. This happens regardless of what player I use. It's been a while since I've played a dvd on here so I tried to remember everything I've done since it last worked correctly. From what I can remember, I built and installed a newer gcc(3.4.4), recompiled my kernel to add the loopback device, and reinstalled the nvidia driver.

My first thought was it could be an Xv problem, since that would be common across all applications, but the output from mplayer seems like it's using Xv and cpu usage looks about what it should be. This only happens with dvd's, dvd's I've ripped play just fine. The only other thing I can think of is it's my dvd drive itself, but that doesn't seem likely since I've noticed no issues reading/writing discs from it.

I'll continue working on it, but in the mean time, any suggestions?

I hate to post a SOLVED so quickly, but I figured it out. For some reason, as to why right now I still don't know, DMA was turned off on all my drives... No wonder Quake 4 was having issues loading textures.