I think godaddy does it as well, and I know that there's at least one more I can't remember right now, as well.
backorder it (free) and if you get it, you'll have to pay something like $59 or $69....if nobody else bids on it during the auction phase.
That's about the extent of my knowledge on the subject. I know the domain has to go through different phases of expiration (total of 75 days, I think) and you can lose it anytime I think within the first 40 days (again, not sure exactly) to the original domain owner. Then there's an auction phase that you can be involved in at the sites above. If nobody else backorders it/bids on it, then you get it for the prices above, depending on the site.