You should be getting a MacBook Pro or a MacBook. For the simple reason that with a Mac you get the best of both worlds. Thanks to Apple's Boot Camp, you can run Windows XP or Vista natively on its own partition and it runs incredibly. They look gorgeous, they run incredibly and best of all you also get to run OS X. So you can experience 2 operating systems each on their own partition. Does it get any better than that?
Macbook: http://www.apple.com/macbook/
I configured one for you and came in at $1474.00 USD
13.3" screen, backlit screen
Aluminum unibody construction
4 GB RAM
250 GB Hard Drive
2.0 GHz Intel Core 2 Duo
I just ordered a new 15" MacBook Pro which will be here on Friday. I'm typing this on a fairly new iMac which is running Windows vista. I have 3 Macs and all run Windows. I actually use Windows on my Macs about 95% of the time. I love the hardware and I like switching to OS X every now and then.
I will never buy another laptop/notebook from a PC manufacturer. Not when you can have 2 OS's running natively. I will say Dell would be my 2nd choice. My main computer is a Dell XPS 720 HC and its really nice.