Im assuming when you once knew them you were an AFC, so do not by any means act with them the way you used to.
Be confident, take the right steps, ignore any statements like "you've changed" and know that your game is good enough to get them
One thing I suggest, if you don't already have one, is a myspace page. It gives you another gateway for women, especially old high school flings, to contact you . Be your new and improved self around them but don't go overboard on routines and such.
__________________ "Take the lead but don't show the need."
You have some history built up, which can make things more comfortable. Even if you didn't talk to her much, you knew of each other and the social circles. 3 years out of high school, some people hang on to their friends, or lose touch with their friends altogether. People fall out, people move, peoples interests change.
It's okay to reference the past, but better to talk about what's going on now.