here are my 2 cents.
first of all....WAIT don't buy a laptop to take with you to college till JULY (maybe even august...back to school sales
) anyway...now here goes my 2 cents:
Mac vs Windows:
Vista is comming early next year, will be quite an improvement over XP, however, not as much of a leap as XP was over Me. Now that said, a similar thing happened in the Mac world just earlier, where OS9 was quite a difficult and not very friendly OS was dumped in favor of what they call X. Better OS by far. Now in comparison to XP and X. Things are done DIFFERENTLY for the most part, everything from software installation to changing settings, even the use experience is different thanks to the lack of a task bar. However, not that its difficult, but does take time to adjust to. Note all your current software will no longer work (...don't even bother VirtualPC or Wine for OSX) but again, not that its a bad thing, you'll be using DIFFERENT software. What I am trying to say is that one is not better than the other, they are just differnet. One advantage X has over XP is the no need to worry about spyware. Stability wise, from my experience they are pretty much the same, that is work flawlessly most of the time but once in a while they will freeze on you for one reason or another.
I went to the apple store and checked out the MacBookPro, big improvement over the prev-gen Powerbook, but 2 things about it annoy me: 1 mouse button, keyboard. I am not saying that just because I dont like the keyboard its a bad keyboard, its just that that i don't feel comfortable typing on it, see how you feel. I also find myself using the right mouse button quite often, and the lack of it on the touchpad is killing me (yeah i know i can plug in a mouse blah blah blah.... but i am not actually gonna do that if i am trying to use it on the or plane for example where there is no room for a mouse). So what I am saying is go to the store and REALLY play with the hardware, make sure that you feel comfortable using it, and that it feels solid and that you like how it looks. Since you mentioned the ibooks, not sure about the current gen, but the previous (earlier G4/ late G3..the first white ibook) where plagued with motherboard problems. Secondly, being white... not a practical color for a computer since it will show EVERYTHING. Silver/gray is the best color in my opinion.
Buying now, by the time you need to take it with you it will be outdated. New technology will come from apple, and from other manufacturers, for example the new Turion X2 which will kick all kinds of processor ass, as well as possibly new faster video cards from ATI and Nvidia.
Other things to consider:
I am not trying to discourage you from getting a mac, but do consider other things that you most likely haven't considered before, seeing as you are a former Dell user, you probably are missing out on a a lot. First of all, check out ASUS and MSI laptops, stylish, powerful, and affordable computers. ASUS is also top notch when it comes to quality (if memory serves me right, they used to build the Powerbook for apple). Secondly, lets look at software, if you're tiered of XP fool around with linux, in the recent 2 years (especially over the last 6 months) linux has really become a fantastic and more friendly than ever OS. I've been tracking linux for the last oh 5 years and its better than it has ever been... a lot better. It will be a big change from windows, you'll get more stability, and just as with mac, you'll no longer have to worry about spyware and virses. And (for the most part...thanks to people at Transgaming) you won't ahve to give up your favorite games.
anyway....which ever way you go is up to you. Make a smart move.