Federal warrant for child support

What is the name of your state? I'm in Texas

I'm posting for a friend (honest) who just found out that his unpaid child support debt has been turned over to the feds. He'll be collected in the next "roundup" done in this area. The reason the amount remained unpaid is long and complicated but he wants to pay it off (he has wanted to for a long time but hasn't had the money -- everyone who knows him is helping scrounge up the total). But...

1. Who would we contact about his outstanding debt?

2. If he pays off the entire amount, is the federal warrant cancelled?

3. Is it possible to pay off 3/4 and then arrange for payments for the rest (in case we can't come up with the entire lump sum)?

He has a two little girls -- 2 and 4 -- and it seems ludicrous that the feds would still take him away even if he pays his debt. But he's afraid to come out and ask so we are all trying to help. He's a good man and a dedicated father. Had he been older and wiser back when all this started he could have drastically changed how things turned out -- the judge who handled the divorce was his ex wife's uncle, and the court clerk was her sister. Needless to say, the deck was stacked against him and he truly was "shafted".

I appreciate any advice anyone can share. We know the feds have had the case for close to 3 months, although we just found out. We want to move quickly before the roundup occurs, to save him and his family all of the trauma that would bring.