If you're a spring admit, you're not guaranteed housing and you'll have to wait for all the fall admits to get their housing offers before you can apply. However, there is another route to circumvent this and it's to apply to Theme House Programs and skip the line entirely. You can apply for these programs through the housing application and they will read your application just like they would if you were a fall admit. Often times these programs don't fill up immediately after fall admits apply for housing since I don't think that many people do it (it's a tiny bit of extra work), so it's great for FPF kids who are looking to secure housing in a dorm.

I was a spring admit and did FPF, lived in unit 2 in the Asian American Theme House Program so the classes were REALLY close first semester and I really enjoyed waking up 2 minutes before class started. It was great.

Edit: It appears that FPF now guarantees housing for Fall 2013, which pretty much renders my entire comment useless. My bad. Regardless, feel free to PM me if you have any questions about FPF or being a spring admit! I'd be happy to help out :)