Did you press ESC on the boot splash screen in order to boot from Windows XP installation CD? Do you have BIOS 205 or newer, so that you can enable the IDE/SATA-compatibility mode - otherwise you need to create a special...
If you are Asus G1S user, you might be interested in checking out the Asus G1S wiki at http://asusg1s.wikidot.com/. You can find following stuff there:
- Installing XP on G1S
- Linux on G1S
- Updating BIOS