Any half-height (about 1.75" tall) 5.25" optical drive should work in the PowerMac. Some of the newer drives are SATA instead of ATA (IDE), so you'd need to run a SATA cable from one of the 2 available ports on the motherboard (meaning you can only have 1 hard drive installed) over to the drive bay instead of reusing the ATA cable that Apple already ran for you.