Setting up aseagate st3320620as for sata 2

What motherboard?

If its Intel based (i.e. X58 or P55), set it to ACHI. Some NVidia mobos have this option too.

If not, set to anything but IDE. Maybe Enhanced, or something like that.

Or are you asking if its SATA I 1.5Gbps or SATA II 3.0Gbps? Still depends on your mobo.