the new generation ( well, anything in the last 2 years or so ) JMicron 's are all 100% AHCI compatible and do a fairly good job of just being a sata interface, and I've not seen a JMicron pata interface in years.. not sure if they even make those anymore.
Well, I admit my inquiry was not CentOS relevant :) Thinstation does not have support for that stuff as it seems! And that is what I would need to use.
jlc