misplayed? where exactly?

-----HAND 1------
Game #1261894163: Hold'em NL ($0.25/$0.50) - 2005/11/07 - 16:36:20 (ET)
Table "Kapelle" Seat 8 is the button.
Seat 1: anna1897 ($50 in chips)
Seat 2: Fazfaz ($49.95 in chips)
Seat 3: firewire ($50 in chips)
Seat 4: dMechaniC ($12.75 in chips)
Seat 5: ScubamanB ($46.71 in chips)
Seat 6: Silvercat ($20.30 in chips)
Seat 7: Dubsko ($50.85 in chips)
Seat 8: bacmor ($28.69 in chips)
Seat 9: biffen111 ($33.62 in chips)
Seat 10: Trevinski ($26.26 in chips)
biffen111: posts small blind $0.25
Trevinski: posts big blind $0.50
firewire: posts big blind $0.50
----- HOLE CARDS -----
dealt to firewire [Ad Kd]
Fazfaz: calls $0.50
firewire: raises to $3
dMechaniC: folds
ScubamanB: folds
Silvercat: folds
Dubsko: folds
bacmor: calls $3
biffen111: calls $2.75
Trevinski: folds
Fazfaz: calls $2.50
----- FLOP ----- [Jd 7c 3c]
biffen111: checks
Fazfaz: checks
firewire: checks
bacmor: checks
----- TURN ----- [Jd 7c 3c][4d]
biffen111: bets $1
Fazfaz: calls $1
firewire: raises to $6
bacmor: calls $6
biffen111: folds
Trevinski sits out
Fazfaz: calls $5
----- RIVER ----- [Jd 7c 3c 4d][7h]
Fazfaz: bets $2
firewire: folds
bacmor: calls $2
----- SHOW DOWN -----
Fazfaz: shows [8d 3d] (Two Pairs, Sevens and Threes, Jack high)
bacmor: shows [3s As] (Two Pairs, Sevens and Threes, Ace high)
bacmor collected $33.75 from Main pot
----- SUMMARY -----
Total pot $35.50 Main pot $33.75 Rake $1.75
Board [Jd 7c 3c 4d 7h]
Seat 2: Fazfaz lost
Seat 3: firewire (big blind) folded on the River
Seat 4: dMechaniC folded before Flop (didn't bet)
Seat 5: ScubamanB folded before Flop (didn't bet)
Seat 6: Silvercat folded before Flop (didn't bet)
Seat 7: Dubsko folded before Flop (didn't bet)
Seat 8: bacmor (button) showed [3s As] and won ($33.75) with Two Pairs, Sevens and Threes, Ace high
Seat 9: biffen111 (small blind) folded on the Turn

I would have bet the flop. I try not to let them see the next card for free in that situation. Here you are third to act with one behind. Bet like you hold AJ. Would AJ check the flop? If they believe you hold a jack they wouldn’t be so proud of their paired 3s.

i wasnt a huge fan of betting into 4 to the flop, but youre right, i was almost last to act.

I would either cbet or check/check/fold.

did u get the name firewire from cosmic gate by any chance?

Don't expect anyone to fold any pair after you check on the flop. Continuation bet against 3 fishies is suicide. The chances of ace-king high being the best hand is unlikley, unless you bet the pot which is $12 you will have a difficult time getting anyone to fold, your check was good.
On the turn you bet $6 into a $14 pot, that is a meaninless/gutless probe bet, its clear you missed your flop, it accomplishes nothing, only options here are: pot sized bet or call his little bet, hes giving you great odds + you have good position on him.

What EricE said.

Bet the flop

WTF The raise on the turn i dont like that at all.

And if the river comes bringing you Mr. Flushy Flush bet out 1/2 pot

Even third to act it's hard to c-bet 4-way. Depending on reads, EP could check raise you, or the 4th could have the J and reraise you out.

Check is g00t. I can see the turn semi-bluff, but you could just call and check/fold the river as well.