$20+2 3 handed, A7o in the BB. Stupid question!

[trevor]

Button doubled through me a while ago after he'd been sitting out (computer trouble?). He comes back in very first hand w/ ~ T1200 and shoves w/ blinds at 75/150. I put him all in w/ A[img]/images/graemlins/diamond.gif[/img] 4[img]/images/graemlins/spade.gif[/img] and he shows K[img]/images/graemlins/club.gif[/img] 7[img]/images/graemlins/spade.gif[/img]. Flop was K K 9. He's playing desperate and like a donk. SB is ok but I have a good read on him. He's awfully weak-tight and has consistantly folded to my raises. We have not been 3-handed long.

PokerStars No-Limit Hold'em Tourney, Big Blind is t400 (3 handed) converter

Hero (t5680)
Button (t4220)
SB (t3600)

Preflop: Hero is BB with A[img]/images/graemlins/spade.gif[/img], 7[img]/images/graemlins/club.gif[/img].

Button limps for 400, SB completes to 400, Hero?

Given my reads I would like to hear what everyone does as far as raising or checking goes.