I think there's a great urban myth built up around the backstory and Lucas' original 'master plan' of having everything planned out when he wrote the original trilogy. A great deal of it seems to be fan exageration, and its very rare to come across anything firsthand from the man himself.

However, in 1999, when phantom menace was came out, there was a very enlightening Lucas interview on the UK morning show 'Big Breakfast', where he spells out the extent of his original plans for the movies. Despite, or maybe because of Johnny Vaughn, its one of Lucas' more interesting interviews.

I've uploaded the most relevant bit here: http://rapidshare.de/files/8285059/lucasBB.mpg.html

Fried Gold.