So I spent some time this weekend playing with the
LDraw parts library along with
MLCAD for designing Lego creations. The the
LDraw parts library seems to have every Lego part you will ever need and then some. I had an easy time picking up on using
MLCAD as it is a lot like AutoCAD in some ways. I also messed with
LeoCAD a bit but found it to be harder to use than
MLCAD but that could be due to my understanding and use of AutoCAD.
If you like Lego's but don't have all of the bricks for your next model/idea this maybe an answer. Until you have the $$ to get the real thing!