I'm in kinda the same situation as you. Although instead of starting at college in september i'm going back to my third year.
My current laptop is a PC. I actually did the unthinkable and went from a Macbook (gave it to my girlfriend) and bought myself a PC. The worst decision of my life, and i can't wait to get back to OSX.
Anyway, i've decided to use the PC untill this year of school ends in just a few months, and buy a MBP before school starts again in september.
As you have guessed, i've decided to go with the Montevina.
Capella/Nehalem will be great i know, but the current Q2 ETA is not at all a guaranteed time of arival.
Montevina could even be dalayed, and the Capella and Nehalem is so far out in the future that there really is no way of telling.
I think we'll see this happening, but bear in mind that this is just my own thougths and that i don't know anymore than anyone else:
Montevina/Penryn 1st revision: August 2008
Montevina/Penryn 2nd revision: March 2009
Capella/Nehalem 1st revision: September 2009
Capella/Westmere 1st revision: April 2010.
Also, if the new CPU indeed is so revolutionary as people are saying, there is a good chance that it will need some time to "settle in".
If we indeed will see mobile CPUs handlinge up to 4 or even 8 cores by the time Nehalem get here, it will take som time to adjust software, and other hardware to fully be able to use the power of the new technology.
The 2nd Capella revision will be the time to buy it for me. And by that time my Montevina MBP will be nearly 2 year old, and in need for an update anyway. (The last couple of years i've replaced my laptop once a year, but i hope (and belive) that the Montevina MBP will last me two)
Thats my thoughts.