From what I recall, LucasForums started when JediKnight.net and Mixnmojo.com decided to integrate their forum systems to create a common community between the Star Wars and original LucasArts game communities.
At the time, I was the founder of Valley of the Jedi, which what a competitor of jk.net, but joined up with LucasForums to help out with LucasGames. That was to be a unified site for all things LucasArts, but ultimately didn't get the following that the individual sites did.
JediKnight.net started in 97/98, around the same time votj.com and mixnmojo.com got going. Man that was the early days of... just about everything internet related