I'm having the same trouble. I cannot get my Plextor to go to DMA in the BIOS. Every time I try it switches back to Auto and disables DMA mode. I enable DMA in IDE properties and it sets itself to PIO.
A check using Adpatecs ASPI check shows that I have no ASPI installed and when I try to install ASPI it says I have no adaptec devices installed.
I saw this Force ASPI download program at doom9.org but it has no install directions so I'm not sure if I need it or not.
Running Win2k, clean install, SP2
I read in another thread that SP2 was supposed to correct the DMA problem with plextor but apparently that is not the case.
In the mean time everything is working right now so should I just leave well enough alone?