DVD and CD-RW drives "lost" by windows

I don't know why, but Windows (2000 and XP Pro both)
intermittently "lose" or forget about my DVD-ROM (Pioneer
DVD-105s) and my CD-RW (Yamaha CDRW 2100E). Both were
recognized when I installed the operating system, then, at
some point, it can't find them anymore.

I have an Intel 850GB motherboard and two IDE hard drives.
IDE 1: Western-Digital (120GB) ATA-133 on Master
DVD-ROM on Slave
IDE 2: Western-Digital (80GB) ATA-133 on Master
CD/RW on Slave
Soundblaster Sound card (with the motherboard sound disabled.
Matrox G-550 video card
Matrox 2500RT editing card

I can't find my drives. Windows says that the drives are
disabled (Code 22) and are causing a resource conflict. I
can't figure out what it is!

When I setup the OS, both of the drives were on DMA-2 and
now they're disabled and the IDE controllers say PIO.

I'd love some help. Sounds like a hardware problem, I just
don't know what it is.