Before you get a Mac, I would check and make sure that they are fine to use by your department.
I've had many a friend that bought a laptop only to discover they should have purchased a mac or should have purchased a PC.
If you are doing graphic design, film, or media, there is a good chance you would need a mac.
If you are doing computer science, engineering, or math, there is a good chance you would need a pc.
As far as the mac goes... I have a macbook pro. I got it in July of 2006. The only time I ever have issues with it is when I am trying to run illustrator, photoshop and flash at the same time. No problems with final cut or running photoshop, dreamweaver, flash, ichat, safari and mail.... It's only when illustrator gets opened that I have any issues. So as far as waiting on upgrades, you probably don't need them.
What I would do is go to the mac store and ask if they have any of the older releases of the 15 inch mac book pros available. If they have one or 2 in stock, they would probably be willing to give it to you at the cost of the macbook. I know when I went in to get mine, I asked what older ones they had and they had 3 17 inch ones that would have been about $50 cheaper than the one I ended up with, but $15 inches was just too much screen for a laptop to me.
Or even see if you can find a refurb 15 inch. If all you are waiting on is the aluminum, you can probably find it in a mac book pro.
Best luck!