laptop for designers, macs Options

[whomps]

So yea, I'm gonna be a freshman in College soon.. and I was wondering what would be the overall best type of laptop to get for my major.. Graphic Design.
Yea yea yea, I know everyone is going to say MAC HANDS DOWN. Macs excite me too, but they're also intimidating.

Basically I checked out the Macbook Pro on the Apple website and it looks pretty damn sick. But I've been using PCs all my life and I'm kinda scared to switch into Macs and get all jumbled and frustrated..

I was wondering if there would be any MAJOR differences switching into Macs, like.. would there be programs that I wouldn't be able to use on Macs that I've used on Windows before ?

ALSO. If I decide to get a Mac.. which one should I get ? Macbook or Macbook pro ?
If you're a designer but you're not looking for anything bulky, what screen size seems to be the best ?

Furthermore.. is there any possibility that getting a PC would be better than getting a Mac for design ?

Hmm.. My budget will probably be.. something under $3,000. I'm looking for something that will not break down on me in 3 years and will not lag or OWN THE SHIT out of me if I have a 20" by 20" 300 dpi psd opened up on the latest version of Photoshop. How much RAM should I buy ?

If you're a Mac user, what are some problems that you have encountered ?

Any help is appreciated. :}