I think in school one of the foremost considerations should be weight. I really don't want to be lugging around 5 lbs of computer on back in addition to all the books. Given that, I think PC wins out.
The thin and light that steps up on the Mac side is the
MacBook Air.
http://store.apple.com/us/browse/home/s ... TM3NDkzNzU
The bottom prices on these are $999 for the 11" version and $1,299 for the 13" version.
These weigh in under three pounds, but are a little light on memory (2 GBs) for running windows.
On the PC side you have a number of options. You could go cheap and get a netbook, but the performance on these is underwhelming. If you were looking to go just a few hundred dollars cheaper than the Mac, you have a few nice options.
Competing with the 13" MacBook Air:
TOSHIBA Portege R705 - Intel Core i5 (2.53GHz), 4GB DDR3 Memory, 500GB HDD, Windows 7 Home Premium, 3.20 lbs, Up to 8 hours - $849
http://www.newegg.com/Product/Product.a ... 6834214024
Acer Aspire TimelineX - Intel Core i3 (2.40GHz), 4GB Memory, 320GB HDD, Windows 7 Home Premium, 3.97 lbs, Up to 8 hours - $649
http://www.newegg.com/Product/Product.a ... -_-Product
Competing with the 11" MacBook Air:
Acer Aspire TimelineX - Intel Core i7 (1.46GHz), 4GB Memory, 500GB HDD, Windows 7 Home Premium, 3.10 lbs, Up to 8 hours - $849
http://www.newegg.com/Product/Product.a ... -_-Product
Acer Aspire AS1430-4857 - Intel Core i5 (1.06GHz), 4GB DDR3 Memory, 320GB HDD, Windows 7 Home Premium, 3.09 lbs, Up to 6-hours - $599
http://www.newegg.com/Product/Product.a ... 6834115954
It is a personal choice. But when you are estimating the cost of the system, take into account what additional software and peripherals you are going to buy. For instance, people have been mentioning running both OSX and Windows. To add Windows 7 Home Premium to a Mac can cost hundreds of dollars.
Windows 7 Home Premium - $179
http://www.newegg.com/Product/Product.a ... -_-Product
If you want to run Parallels, it is another $79 dollars.
http://store.apple.com/us/product/H2481 ... TY3ODQ5OTY