I'm sorry for being rude, but the answers you seek have been posted here so many times because people havent' searched or taken time to read the sticky posts I referred you too. If people would search instead of asking the same questions over and over, the answers would be easier to find.
If you read the docs I referred you to, you will understand why using pkg_add is not the correct way to add stuff on FreeNAS 8, because the next problem you will be posting is "Why is my root partition full?" which is also answered in the docs.
I have seen the problem before, too many times, and my HELPFUL answer is to read to docs :)
The first 3 posts are sticky posts, they have the answers and more....
http://forums.freenas.org/forumdisplay.php?5-FreeNAS-4-N00bs