reinstalling windows xp

Hi, having problems trying to reinstall windows xp on my macbook. Reading on the microsoft support pages it says you need to boot from the startup disk to do the system re-install, but I can't seem to do this. I tried to just leave the disk in, then restart in windows, but it just spit the disk out. Then I tried leaving the disk in and holding down the option key and clicking on the startup disk, then all I got was the blank windows screen with the line in the corner. Any help on how to do the reinstall???