A9 or lower:
With 6 players, I'd play it VERY carefully. Maybe limp in as was stated (in early position). If I get a good size reraise back at me, I'm probably going to fold.
With 6 players,
odds are just too good that there are better
hands out there. As was said, what could you hope for on the flop - what are you looking for?
Any A pairs you up, but also pairs up someone else. With 6 players, odds are good (especially if you were reraised) that you are beaten. If everyone checks to you, bet a SMALL bet and see if you get a reraise. If no reraises, maybe make a good size cont bet on the turn. The only thing that makes you confident in your hand is 2 pair on the flop (pair up your kicker). With A2, I maybe call a small reraise relative to my chip stack hoping for a Str8 or Str8 draw.
With A10 and up, I still limp in, maybe small reraise, but then I'll play it more agressive if I paired it the A. I'll bet enough to announce I have the A and see if I can win right then, but I won't bet so much to leave me crippled if someone has me beat.
Anyway - as the table gets smaller (3-4) I play it a little looser.