Why's my DVD playback so poor?

HTPC is not that important a consideration for me since I don't have a projector yet and my main setup is fine otherwise, but I wonder if anyone can explain why DVD playback is so poor on my system. It was never intended as a DVD player, so I'm not upset, just wondering where the problem lies:

Abit BP6 dual celeron board running 2x400 celerys o/clocked to 500
256 MB PC100 Mem
Dell PERC UW SCSI Raid Controller running 2x striped Western Digital Enterprise 7,500 Rpm disks.
Early model samsung DVD (IDE unfortunately)
Viper 550 PCI (16MB TNT)
Using Ravisent Cinemaster 2000 on Windows 2000 Server (but all absolutely non-essential services are stopped for DVD playback, idles at 1-2% CPU time) (I need server because I develop Active Directory applications).

Most DVDs are unwatchable - extremely jerky. I've tried every setting and tweak imaginable. I know the graphics card is old and probably the bottleneck, but I would have thought the 2 celerys would have coped better.

Any thoughts? Thanks.

[Branxx]

I have a similar configuration on my home server (Asus P2B-D, dual P3 500Mhz, IDE DVD drive and Windows 2000). This works without any glitches.

One thing to try is to check Enable DMA transfer for the DVD drive. Windows 2000 disables this on installation.

My software player of choice is PowerDVD.