It is very common for old high school friendships to cool down over the years. As others have said, start slow and small. You may find they just aren't receptive because they may have kids, a boyfriend or a demanding job.
I have to echo Venus on Meetup.com. Prior to moving to MN from AZ, I heard that MN is tough social nut to crack. Boy, was I right. The people are nice enough, but really aren't interested in new friends.
We joined several meetup groups according to our interests. About 95% of our friends are through meetup and the rest either friends of friends or from dh's work.
Take a look at meetup. Seriously. Do you like to knit? Do you like going to the pub and socializing over a beer? There is definitely a meetup for you. Put yourself out there and give it a shot. I would hate for you to spend all your time and effort on long time ago friendships that may not rekindle.
I have met some amazing people on meetup... and don't get me wrong, there have been some weirdos... like the gal living a double life married to two people at once. Other than that, we have made some fabulous friends.