IMO, there only 2 reason you need a Controller Card
1) you ran out of IDE slots.
2) you gonna RAID (which is not that necessary)
a ATA66/100 controller card isn't gonna make it any faster, unless you have 2 top of the line IDE hard drive under the same controller, then you may see some bottleneck in a ATA33.
a good ATA66 controller card is Promise.