There were some girls from my high school who were total witches who joined sororities. They were at different colleges so it really didn't matter.
There were 3 girls from my high school at my college who were not witches, but as you said, concerned with being popular. 2 joined one group (the "most popular" one) and the other joined a different one. None of them joined my group. One time the third girl made a crack about me being geeky in high school to a fraternity guy who happened to be a good friend of mine (and who also was slightly scary if you didn't know him well). He proceeded to rip her a new one. It was awesome

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So the moral of the story is...unless you're going to college with everyone from your high school....don't worry about it. A lot of times the people who have been coasting off the "popular" image they attained in 7th grade get a VERY rude awakening when they get to college.
Oh, and drunk guys will hit on you EVERYWHERE at college - Greek or not - if you don't like the idea of that, either 1) don't go to a coed college or 2) don't go to parties.