Nice mainboard, 4 ATAPI connections!
The 'UIDE' ports are for your high speed Ultra IDE hard drives. You connect 80-line Ultra DMA IDE cables between the UIDE sockets and your DMA-66, 100, 133, or faster hard drives. You connect slower devices like CDROMs and older hard drives (DMA-33 or slower, and PIO only drives) to the other two IDE ports. DVD drives may run better on a UIDE port.
Make sure your BIOS settings enable the high speed drives.