Most CD-ROMS are capable of supporting DMA mode, but the default in XP is still PIO. Setting it to DMA won't make your CD-ROM faster, but it will consume less CPU cycles. Here's how:
1. Open the Device Manager. One way to do that is to right click on "My Computer", select the Hardware tab, and Select Device Manager.
2. Expand "IDE ATA/ATAPI Controllers" and double-click on "Primary IDE Channel"
3. Under the "Advanced Settings" tab, check the "Device 1" setting. More than likely, your current transfer mode is set to PIO.
4. Set it to "DMA if available".
Repeat the step for the "Secondary IDE Channel" if you have devices attached to it. Reboot.
For a Microsoft article on setting the DMA mode Click Here.
(Note: You will not see the Advanced Settings section if your hardware does not support it)