[nightlyraver]

First consideration: If you are worried about overcards, you are actually taking the worst of it preflop since chances are that an overcard will flop. Folding 99 out of position is not a bad play is you are not comfortable playing post flop. Calling is fine if: you don't mind one overcard on the flop that isn't an A; you feel that you can successfully check-raise Villian when you are likely ahead.

Second consideration: If you do not feel that Villian will bluff with a hand like AK a decent amount of the time, you should bet this flop and fold to a raise.

Third consideration: Once Villian bets, you have to follow through with your plan. Since an overcard WILL fall on the turn (usually) you should not give Villian a chance to catch up. Raise enough to severely price him off his A-high hand. If he has a bigger pocket pair, you simply do not have enough chips to get off the hand. I would simply move all-in at this point OR make a pot-committing bet that he MAY call with AK (perhaps 1,900). Note that you CANNOT fold when the A hits if he does call since you are pot-committed. To avoid any tough decision, just go all-in.