Erik Reid, you wrote:

> But then I plugged in the machine's main disk, and it seems to be doing ata/66(all the
> drive supports) just fine. :|

I have a similar problem with the Promise PDC20265R (ATA 100) on the
Asus A7V266E mainboard. Neither my CD-RW nor my DVD-ROM can use (U)DMA
when connected to this chip. Limiting 'cd* at atapibus0' to PIO mode 4
lets me work around the problem.
Someone suggested, those Promise controllers (or at least the onboard
chips) are only supposed to work with harddisks, but I am not yet
convinced.
See PR kern/17642 for more details.

ciao
     Klaus