fist question is your hdd ata 66 or 100? important because while you can run your ata100 hdd at ata66 rate the converse doesn't hold true for an ata66 hdd.
put your hdd on the on board promise controller ide & the promise bios will show you what udma your hdd is detected at (udma2= ata33,udma4 =ata 66, udma5=ata100). if you leave your hdd on the m/board ide controller then your limited to udma4 max!