Am I right in assuming you can mix IDE and serial ATA hard drives on a motherboard that is equipped for both?

Yes, you can. I'm doing so at home. The question is... which set has the boot drive? I have two 120GB drives in a Mirror RAID as my boot device (SATA Drives) and added another 120GB drive on the IDE chain. Most motherboards will default to try and boot off of the IDE chain, so if you have your SATA drive(s) as your boot device, you'll wanna go into your BIOS and make sure you have it set as the drive to boot off of.

Thanks for the info. I've three IDE drives at the moment and two (40gb)are going to be retired to be replaced by a 160. I usually go with IBM but am trying one of the Seagate Barracudas this time.