Well, if you're a student, then whatever is available at your computer labs should probably be what you learn. :tongue2:
The industry standard for mechanical engineering is Pro-Engineer. In my opinion, it isn't very user friendly, and is a bit of a pain to learn, although their latest edition: "Wildfire" is getting better.
Pro-E has the ability to do finite element modeling through Pro-Mechanica which is an add-on.
Solid Works and Solid Edge are two middle-of-the-road packages. I haven't used them personally, but from the demos I've seen they seem to be much easier to learn, but may not be as powerful as Pro-E.
Catia is another high-end package used almost exclusively in Aerospace and Automobile applications. I think Boeing and GM use this software. It looks incredibly powerful, but the ticket price is enough to make any small company blush, let alone a student.
I'm not sure what they use in typical structural engineering firms.
If you have to buy something yourself, and a student version of a real solid modeling package isn't available to you, you could always give AutoCAD a run around the block. It's got solids capabilities which would let you learn how to build objects in 3D. The real drawback is that plain-old autoCAD isn't parametric, meaning once the object is designed, you can't go back to modify any values. On the other hand, AutoCAD is the industry standard for 2D drawings, and definately is much better than any 3d package for architectural type work or space planning.
Go for Pro-E then. Wildfire if you've got a choice.
Hit the library or bookstore and pick up a $20-30 tutorial book. The stuff I've found when doing internet searches is either garbage or geared toward those with some experience. Even better, ask your friends to see if anyone's got rudimentary knowledge and is willing to teach you. It's a bear to learn in a vacuum.
Oh... I thought that the school had it available when you said that you saw people using it.
Learn what's available. Pro-E would probably be better to know in the long run, but the main thing to learn (which any package can teach you) is how to visualize an object and how to figure out how to build it up in virtual space.
Another package which has a large following at my school is I-DEAS. I'm not a big fan, myself... the final results look too cartoony to me (their color scheme really stinks... oranges and pinks). There's almost no comparison to some of the stuff my senior design team turned out in Pro-E. I'm probably judging a book by its cover though.
Alright. Enough from me. I'll get off my soapbox and let someone else get their $.02 in.
I used CADKEY when I was in school, and played around with AutoCAD, both retail for around $3500 now (back then the retail was lower and the student edition was like $150, might want to check it out). SolidEdge and Esprit seem to go for around the $5k mark depending on what options you want, still pricey stuff and each have their pros/cons. I actually liked CADKEY on DOS, your hands barely left the keyboard and it seemed much faster that way.
As an alternative with a very easy to use interface of a nearly CAD-level program, Rhino is something to consider and the $900 retail and $200 student price are quite attractive. Free trial download is good for 25 saves. http://www.rhino3d.com/
Also, a year or so ago a free version of Pro-E called ProDesktop was available but discontinued. Not sure what the pricing is, but may be another option for you to investigate.
It has been used in the gaming community for years to make car models (and more) for games like need for speed, 4x4 evo 1 and 2 and many others. The last version I used was pretty buggy but from the quick glimpse I gave the site, it seems to have improved a good deal.
Also, if you can use linux it has a few GNU 3d modelling programs as well. Again, not industry standard, but free and something that can atleast get you in the swing. My brother learned with zmodeler, and can apply almost everything he learned to using cad or a few other programs he uses (which are industry standards, I just don't remember them)