how fast does a computer need to be to playback DVD files smoothly?

Can anyone recommend some specs....

I get much better performance playing files back in Power DVD as opposed to Windows Media Player - i am running Windows XP - but still I can't play things full screen and the audio is often out of sync even in window playback, i know this a performace issue because if i burn an SVCD, everything is in sync on my set top DVD player.

i have a 800mhz Athlon TBIRD, about to get a 1.4ghz...
I have a Matrox G450, and 384mb of RAM, and 7200rpm drives, everything set to DMA.

does a mpeg 2 hardware accelerator help playing back any mpeg 2 file or just DVDs?