Wow. I have a psych background and I'll tell ya... Reading some of these posts, I should set up an on-line course "She likes you, dude!". Women, are more complex in the way they approach these things. They don't just bar up and slobber. Nooooo!
Women have a HUGE variety of ways in which they will flirt. Some are verbal, most are physical. A tilt of the shoulder, a finger twisted through the hair, crossing her legs toward you, physical contact, wetting the lips.... FUCKING BLINKING!
The main thing to remember in successful flirting is... FLIRT BACK! If you show no passing interest, a woman will stop being interested in you, quickly. There's the occasional girl who finds the ultra shy or stand offish guy ultra sexy, but they're the exception. Confidence is crucial.
So, here's a physical flirt tip. If you think that a girl across the room might like you, look but don't stare. When she meets your eyes, take around one second, look a little supprised, then instantly embarrassed, glance away. Now, don't miss a beat. Look back at her smile, shrug and mouth the word "sorry". Even if she's not interested, chances are you'll make her feel good about herself. Flirting gold.
*DISCLAIMER* RESULTS MAY VARY!