[ubuntu] How to remove Ubuntu and re-install Win7?

basically, i had windows xp on this laptop and wanted to try ubuntu.
i installed it and stupidly did not keep xp when it asked during the installation.
i did not like ubuntu so wanted to put win7 on it.
when i put in the win7 disc and tried booting from it, ubuntu just loaded and nothing happened.
im not really sure what to do?

thank you