Take care - not all motherboard will accept newer drives, as I discovered to my cost. Some older boards are limited to 2.1Gb on a single drive, and there appears to be no way around it. You can't even use the first 2.1Gb of a 3.2Gb drive. Another break-point occurs at 8.4Gb and this is likely to affect any motherboard since late 1998.
The best solution is to junk the motherboard or switch to SCSI, but Promise makes an alternative ATA-66 PCI card which gets around the problem. The only problem left is that it costs only slightly less than a new motherboard.
Don't get hung up on ATA-66 - it's not going to be any faster than ATA-33 for some time to come, as ATA-33 can easily keep up with all the drive hardware on the market at the moment (unless you get really silly)