This is the article that the NCPA once published. It's a good general introduction to packet. Larry was one of the main packet BBS sysop's at the time he wrote this for the packet community.
Glen Elmore is a microwave engineer with Hewlett Packard and has done considerable research and development in the field of high-speed (>100kbps) digital radio design. His page contains notes on his results so far and pointers to other related information.
Bob Wilkins N6FRI has been involved in UHF frequency coordination in Northern California for many years and has gathered lots of relevant information in his home page.
NARCC is the repeater coordinator for Northern California and works with the NCPA on band plans in the region. (The NCPA and NARCC both cover the same territory, roughly the northern two thirds of California.)