Kjodie, the problem with using just t-posts is that the fence has to be tensioned up tight so the hogs can't push under it. If you're going to make a circular pen, the t-posts would have to be set very deep, say about 4' so the fence wouldn't pull them out of the ground.
Also, you would need to put the posts closer in together. Not every 2' like ZooGuy seems to think, but at least ever 6-8 feet.
Aside from that, the force of the tensioned fence would most likely bend the t-posts in to the point where the fence would become loose could be pushed under.
I'd love to tell you that it would work, but in order for that to happen, you'd have to put in some heavier posts or put in braces to pull from. But once you've done that, it would be easier and cheaper to do t-posts and panels for a small pen. Now if you're looking at a larger pen, say 100' x 100', that's a different story. But in my opinion, it's just not practical for this kind of job.
As exclusion fence, nothing will beat it. We've got literally hundreds, if not thousands of miles of this fence up for hog control around the country, and it works great. The guys calling it chicken wire, saying that it's flimsy, or that you need posts every 2' with boulders attached just don't have any real experience with it. And guys, I don't mean anything buy that, and I'm not trying to start anything, so please just take it for what it's worth. I just make a living putting this stuff up and talking about it every day, and those are common misconceptions.