ubuntu linux is stupid easy to install and run, comes installed with open office and gimp and suduko and mahjong. and terminal server if you need to actually work. (gimp is a great, or nice and capable anyway, image manipulator). try wine (windows emulator) if you need some windows app.
get an ssd (solid state drive). smaller ones are getting cheap, install your os on it and boot up lightning fast.
try ubuntu. dual boot ubuntu/windows. 64 bit version if you have the ram.
