I agree with OME. It's a good place to start. If he's a really good artist he might get bored with some of the limitations you get with free software. Not that it's crippled but that they often lack more advanced capabilities. I too like Rhino. It's not as expensive as 3ds Max or Maya and it is a different way to model based on NURBS. Don't worry about what NURBS are at this point. Main thing is to get him going. He'll branch out and discover the perfect software as he gets better and better.

Also, he's a student so do a search for "academic software." Sometimes you can pick up software that costs a few thousand dollars for a couple hundred. They are full versions and just not supposed to be used for commercial purposes. So unless he's setting up a 3d printer sweatshop, he'll be ok. I like the way Autodesk Inventor works. It has a learning curve but it's really powerful. However, if you want a commercial version it's really expensive. 123D Design uses some of the theory of Inventor which makes sense, since both of them are Autodesk products.

3DCoat is a fun software and is not really too expensive. It allows you to work in a "claylike" environment. You push and pull the surfaces around. If you know what ZBrush is, it's similar. I think it's around $350. That's cheap considering that 3ds Max is around $3500.

But for now, stay simple. If he gets into it, then upgrade him. Below are some links that might help, or, confuse...depending on how you look at it. If you don't want to think about it, then 123D Design will certainly give him plenty of work to do.

http://www.3ders.org/3d-software/3d-software-list.html
http://www.shapeways.com/creator/tools

Here is the link to 123D Design: http://www.123dapp.com/design (ooops...I see OME has this above for you...sorry) It will also print directly to 3d printers but the list is not that long yet. Yours may not be on the list and I'm not sure how hard it is to add a custom printer. Also, check out the other Apps there. They have some fun ones.

Finally, if you want a truly powerful 3d program, one that pros use, look at Blender. It's free as it's open-source. It has a steep learning curve like Max and Maya but you can do anything you can imagine with it practically. I'd say download it anyway and while he plays with 123D Design, he and tinker with Blender and see how they compare and how Blender takes it to the next level. Plus, he'll be able to have fun animating in Blender and doing other fun things that you can't do with 123D Design.