Review of the N4B2
here.
1.66GHz Atom, 1GB RAM (looks like a SODIMM slot on the motherboard, so probably could be upgraded to 2GB RAM, maybe even 4GB although that might be expensive).
The question is, will it boot from USB, as this is usually the best option for booting FreeNAS. According to
this blog article the stock Debian Lenny based OS is installed to a partition on your data disks, and not NAND on the motherboard which may be a good thing.
What I'd do first is remove all 4 disks and try booting FreeNAS 8.0.1-RELEASE from a USB stick, see how far it gets (does it have VGA output? If not, will make debugging the boot process more difficult).