two different girls? did they arrive in a old beat up car and was one of them wearing an old pair of air jordans? if so, go for it... word is is that they're looking for a place to stay. you may get free pizza out of the deal. try craigslist's missed connections or something. don't read too much into people saying "how you doin'".
If a girl comes up to you and says hi first, this doesn't imply anything... at all. But if you interested, just try to get to know her first, then make some sort of move.
I totally agree with everyone that says to be confident. "Hey baby, why don't we go back to your place and play Pearl Harbor?" "Play Pearl Harbor?" "Yeah baby, I lay down and you blow the **** out of me"