Hi,
If I understand correctly, what you want to do is use the two RAID IDE ports (3&4) as two separate standard IDE channels.. with absolutely no RAID..
I haven't used this particular board, but on others with onboard RAID that I've seen, there is a specific BIOS setting to switch the RAID chip from RAID to IDE/ATA-only mode. The setting is separate from the one that enables or disables RAID. It should be under 'Integrated Peripherals', but I don't see any sign of it in the online manual at iwill.net.
I think the fact that this is enabled or disabled in the BIOS suggests that trying different Windows drivers won't help.
Did you try any of the methods suggested here for the kk266r (it uses the same AMI MG80649) raid chip as the KA266R, I think -
http://www.x-faqtor.com/KK266.htm#How to Use Raid Ports as Normal
"...You can also use it as two additional ATA-100 channels for IDE device...."
http://www.overclockers.co.nz/ocnz/mobo/kk266r/2.shtml
AMI's site seems to have zero documentation for the MG80649... doesn't even exist, apparently... that really sucks... especially since they've printed the site address on top of the damn chip.
MC