as far as windows - i spent a summer working in as a compusa business sales rep, so i learned a lot of this stuff ... there are bugs in everything, but windows is pretty solid. It's better than any of the other options for most people; one thing is that you should back up files, and format/reload every once in a while. Stuff gets cluttered and causes problems like you mention.
Laptops - same deal as before, i sold them by the dozen to corporations. Best brands? Sonys are great, very solid, look good, high-line performance, good support. Can be sort of expensive, but the price is dropping, they're very light too. Also, Sager makes great laptops. Gateway and Dell are in the same class as Sony and Sager too probably - it just depends. Gateway and Dell are more expensive, but fully customizably (as far as laptops go), Sony is more limited in choice but not performance, Sager is cheap and makes great stuff but smaller company (= less service etc).
Stay the hell away from Compaq, HP, Fujitsu, and basically any other big-name brand; they have higher dead-on-arrival rates, and have a terrible reputation (HP's bad rep is only in this catagory).
IBM and Toshiba are decent; they'd be in the middle, b/w the other two catagories. I'd go w/ the other ones listed above.