Does it FEEL like PIO mode? There have been a quite a few instances where PIO mode is misreported in Windows 2000... Meaning it is really in DMA mode, but it just does not say.
What usually works is installing the latest IDE chipset drivers for your motherboard, update your BIOS with the latest version and install the newest service pack for Windows 2000 (SP3).
First, I would try uninstalling your IDE chipset driver, all IDE channel drivers, and all of your IDE drives through device manager. Restart and it will install the default drivers, check them to make sure they are in PIO or DMA mode. (They should all be in PIO mode). Then set them to autodetect DMA and reboot once more.. This usually causes Windows 2000 and XP to detect DMA properly.