Asus made an effort and delivered very good and useful manual with EEE PC. In manual you can find detail description of how to install XP and how to customize it for best performance. By customizing we mean how to turn off all those unnecessary, by our opinion, Windows services which take up 4 GB on SSD (for example "System Restore" service). Average installation of WinXP Pro SP2 should occupy around 1.5 GB, exact same amount like our installed OS takes. To be honest, this could be reduced if you use nLite program.