what motherboard do you have right now?
newer drives are either ata100 or possible ata133...which means that your "normal" IDE controllers probably won't allow you to run at those transfer speeds...so you would have to buy an ata100 or 133 controller card, and plug the hard drives into that. also, you will need to make sure you get 80 wire IDE cables, since the "normal" ata33 40 wire cables will not allow those speeds.
this is all, though, dependent on what mobo you have