Are all the system IDE's used up?
I have an OEM MSI board (Medion MS-7091) that only has one IDE, but the normal ones should have two.
Depending on the other load on the PCI BUS (a pooled throughput of 133MB/s), it may be better to use a SATA converter, as the SATA is fed from the chipset interconnect, and does not impact PCI bandwidth.
If there are no other significant PCI bandwidth hogs, it doesn't matter, but what once looked like unlimited througput compared to the old ISA bus, is now looking like it could reach saturation with, lets say, two fast drives and a capture card.
If you have the kit available (and a spare bay!), then you may as well use it, as the average system will not (YET) be in PCI throughput distress - though it would be if the majority of onboard stuff was still "onboard PCI" and not tied directly in to the chipset interconnect (in the case of PCI-Express chipsets, maybe at the PCI-Express level where there is 250MB/s thoughput per single lane device - UNPOOLED).