Take a look at my first DMA link.
Chances are, your optical drive(s) should display Ultra DMA Mode 2.
These most likely are on the secondary IDE channel.
Note: your hdd is probably U DMA 5 or 6.
If it still not resetting to the correct mode, you're on to the #2 link.
When xp encounters CRC errors, it will step down your transfer mode (rate of data transfer). The maximum number of allowed CRC errors is 6, after that, you're stuck in PIO.