Scantool Programming Information?

[mycarsucks]

Well, this year, I have an independant study with a computer emphasis. I was looking for a way to have it tie into my new TR. Then I thought that programming a scantool would be a great computer/automotive project for me. Problem is, I can't seem to find any sites or books that would help me get started. Im not worried about the programming side of it, I need to know more about the frames sent from the diagnostics port, how to grab them, and how to read them. Any help would be appreciated.
Ryan