Since your system disk is also a sata one, onboard sata is enabled in the bios settings. I don't think there would be another setting to adjust.
There's a page in the bios where you'll see all your devices listed (HDD, cd-rom, ...) and you new disk should appear there. Should also be an option to autodetect the hard drives.
There might be a jumer on your SATAII disk (I believe not all disks have one), try to play with it and see if that changes something :
http://i58.photobucket.com/albums/g2...ecteursata.jpg
And yeah, SATAII is not supported by your motherboard. From my experience, a SATAII disk should work on a SATAI motherboard (with the possible jumper set as SATAI), only it will be limited to SATAI speeds, which shouldn't make a big difference. I'll wait for someone else to confirm this however.