this is my first post here and i just decided to post since i saw that you've not received your solution yet. i figured an easy way to change from pio to dma, and i know pio can be extremely frustrating. i had to format each time this happened before i saw the simplistic trick to revert it back.
now, let's get to the point. to revert from dma to pio, all you need to do is uninstall both the primary and the secondary IDE channels. i assume you know how to do that, but here's the how-to anyway.
1) Right click on My Computer
2) Click on Device Manager.
3) Expand the IDE controllers and right-click on the secondary IDE channel.
4) Click on uninstall.
5) Do the same for the primary IDE channel.
6) Now restart your computer.
after you restart, your drivers should automatically reinstall, and the transfer mode should have reverted to Ultra DMA Mode.
hope i helped,
edit: i'm not sure if the rules here permit bumping such an old topic. if they don't, i apologize.