Thanks,
I actually have a working Steam API script made by Jonas Freiknecht. I have it working to set achievements, and there are commands in it that appear to set the leaderboards...

www.schmidt-gallery.com/Stuff/Achievements_Tutorial.zip

It has a bunch of commands in the included steamgs.h file that interact with leaderboards, but I'm not entirely sure how to use them in Lite-c, and I have not heard anything from Jonas. I guess I may have to start from scratch, but I am going to see if I can get these to work first, since they do work with achievements.