Can anyone recommend a good cad tool for the pc? It will have to be easy to use as the last 3d program I had I couldn't even make a box!

Pro/Engineer. I teach teenagers to use it day in day out and they seem to have no problems using it...

Student and educational versions are available free or for a very small amount of money.

JC

Cool does that come with stress analysis and torsion things?

I prefer SolidWorks. That has a free add in for stress analysis called CosmosExpress, which is a stripped down version of Cosmos.

But, be warned, if you are using FEA tools you MUST know what you are doing. Its very easy for a very inteligent person to get the wrong answers out of it. I use it occasionaly for very basic parts with very basic loading, any more complex than that and if you want results you can trust then you should be getting an expert in to do it.

And try to use testing to back up your FEA results.

Errrr, I don't know what I'm doing.. What I'd like to do really is build a frame and find out if it'll crumple in a shunt or twist itself in half when you boot it without the risk to life and wallet lol

In that case, its a waste of time even trying. (not being rude)

That sort of thing is only done with someone with many many years experience and with a very powerful computer and lots of very expensive bits of software.

As said, I can use FEA to stress a single plate or bracket. Anything more than that then I know that my ability is not enough, so I don't try and kid myself I can do it. Unfortunatly I know some people who don't have that sort of self restraint.

Simulating crashes and shunts is nigh on impossible unless you have a specific impact modelling package (LS Dyna etc). You can get a vague idea how it might behave, but it will be not much more use than an educated guess!

Fair enough, I was looking for something with a bit more authority than "I don't think that'll bend so easily"

Scale balsa wood model is the best way. Very easy to add/remove tubes to see what effect they have on stiffness. Just grab the suspension pickup points and twist - gently to start with.
Glue on some cardboard for the floor/side panels for bonus points