Yes, FCS2 will run fine on a top-line iMac. I run it on my 2.16GHz C2D with 3GB RAM with no issues.
Look at the leaflet/booklet that came with old FCP 1.2 disc. It will say "ACADEMIC" in the product key information if it is an academic version. Besides, I don't think the 3.0 upgrade would have even installed if it had detected an academic version of 1.2. So, I'm pretty sure you are fine.