Linux is a good alternative, a lot of real smart and hardworking folks making it better all the time. It is nothing like it used to be. You can detune windows, but first make sure you have plugged a kill-a-watt into your printer and monitor, etc. The effort involved with detuning windows could be lost when MS decides to pull the rug out on you though, and having to get a new registration key when you mess things up is a PITA.
Course there is also the XO laptop, which wouldn't even exist without linux.
One Laptop per Child (OLPC): Laptop Hardware > Specs
It could be kind of trendy to press an XO into service
Myself, I have an old 400mhz laptop I still use everyday (XP).