Odds of Getting In
Getting into the U.S. Justice Department isn't a breeze. It's actually very competitive, despite the low pay.
Plan on acing the bar.
Also work as a judicial law clerk or a prosecutor at a law firm for a year or two before you apply.
However, your odds of getting in are best if you apply within five years of graduating law school, and re-apply if you aren't let in the first time...or the second or third time. Sometimes it takes several tries before you get the job (source).
Things are looking a lot better since the DOJ lifted the three-year hiring freeze in May of 2014, but it's still going to be a challenge to get in and play with the big boys.