[CentOS] Buggy SATA detection w/CentOS5 + Intel H6300ESB?

I've been handed a Supermicro system that is using the Intel® H6300ESB 
Serial ATA Controller (Supermicro P4SCI motherboard).  When I install 
CentOS5, everything seems to work OK, but it has absolutely horrid disk 
performance.  Upon further inspection, it seems that the SATA disks are 
being treated as legacy IDE devices using PIO.  Gah....

Has anyone else had this problem?  I recall having similar problems last 
year sometime with some Supermicro systems, but I can't seem to remember 
how I fixed it.  :-) 

Any suggestions would be much appreciated.

Best,