Catia is one that is used quite a lot. I'm not using that though. I'm using something called ProE at the minute (Pro Engineer). You can learn these simply by doing tutorials and messing around so not that hard I'd suggest starting off like this and if you find it too challenging you can get tuition if you like. Pro Engineer is cool, can simulate a lot of things on it too. I'm using it to simulate stress/strain analysis on a piston at the point of combustion.