The best idea is to buy a copy of XP. You then enter bios (by pressing delete or F1 whilst booting)and set the boot order to CDROM as first boot option. Put the XP disk in the drive and it will boot to setup. One of the options available is to remove any previous Windows installation. Take this option and XP will remove Win 2000 and load XP fairly painlessly - just follow the on screen instructions.