I tried to install the drivers for the Highpoint 2320, but after spending a full day on it(literally about 12 hours), I gave up. Being that I am fairly new to FreeNAS and FreeBSD, I think that the reason I couldn't use it was because Highpoint drivers were for version 7 of FreeBSD. Every time I would try to load the driver I got an error. If you look at the Highpoint website the driver says it's compatible with FreeBSD 4.3 to 7.0. Since FreeNAS8 is built on FreeBSD 8 I abandoned my attempts to get it to work.
After I couldn't reuse my 2320 I bought a 3Ware 9650se-24M8 so I could run 24 drives. I bought it on ebay for $500. I know... it wasn't cheap and everyone recommends against RAID controllers, but I had little choice as I couldn't find a way to fit 24 drives into a system effectively without a RAID controller. Ultimately the 24 port RAID controller worked fine setting up the drives as a bunch of 1 hard disk arrays so it would simply pass the hard drive through.