I have been considering a similar dilemma. I am an accountant, so I ran the numbers:
1220 (low end Macbook with corporate discount)
70 (tax)
220 (full copy of vista)
That brought the total to 1510 for a basic Macbook setup. I have to have Vista for Rhapsody, a few games, and some work related apps.
I decided to go with a Dell Studio 15. For 920 (with corporate discount, 999 retail), I was able to get the following:
2.2 GHZ Centrino 2
4 GB RAM
15.4 WLED Panel
320 GB SATA 5400 HD
256 MB ATI Video
Integrated Audigy Sound
Dell beats the Mac in processing and hard drive. Dell has more RAM, but Mac has better RAM. Bigger panel is better for me as mobility is not a factor. Mac has better video, and Dell should have better sound but it is almost negligible. Dell also comes with 2 year in home service and phone support beating the Mac hands down. Mac beats the Dell in style and design, but these factors are less important to me. I wanted substance over style, and I also wanted to have an extra 500 bucks in my pocket. At the end of the day I got a laptop, digital camera, some extra software, and had a nice dinner for the price I would have paid for the Mac.
I also considered that I would spend a half day formatting and reinstalling Vista to get rid of all the bloatware, and configuring the system for optimal performance. I am an advanced user so this was a minor issue. Additionally, now I have the ability to dual boot the Dell with Ubuntu and run it natively. With the Mac I would have needed to triple-boot, which is not an easy task, or run Ubuntu virtually which was not really something I wanted to do. My advice is, do a thorough assessment of your needs and the costs associated. In my case the Mac costs 50% more and I don't have the need for a great deal of mobility. Don't just buy the Mac because it is a nice looking machine and "everyone else is doing it".