iSCSI is basically bus level communication over the network. AFAIK you can't have a win7 initiator with a ZFS target since the initiator needs to 'speak' the filesystem. While you can have multiple initiators per target, it doesn't work with normal filesystems;they'll think the filesystem has...
That build is way overspecced for a nas box, the zacate boards work fine if not well and 4 gigs is ample ram. I think you'll find bsd's samba performance less than satisfactory (freenas, freebsd, ...) even with tuning. Having done a similar thing myself, I settled on solaris. You need so little...
Every 10.0s: zpool status|tail -n 14 Tue Apr 12 00:44:34 2011
scan: scrub in progress since Mon Apr 11 20:22:49 2011
4.91T scanned out of 6.21T at 328M/s, 1h9m to go
88K repaired, 78.94% done
config:
NAME STATE...
I've tinkered with a rather similar setup for the last few weeks, having tried freenas and freebsd 8.2 and settled on solaris.
I had performance trouble with samba on freebsd so I didn't even bother on solaris; cifs works really well but permissions are a pain in the ass with it, my advice is...