iMac stuck on Windows Vista installation!!!

Hi, ive just tried to intall Windows Vista with Boot Camp.

I went through each step and then my Mac restarted and i began installing Vista, i agreed to the terms & conditions then when i got to the "Where do you want to install Windows" part, i was given 4 choices, but i cannot click on any of them one of the Disks say Disk Partition 3 BOOTCAMP

When try to click the one ive chosen i get a message that says "Windows cannot be installed to this hard disk space. Windows must be installed on partition as NTFS"

Ive tried to quit the installation but the Mac restarts and loads up the Vista intallation again. Ive tried to eject the disc using the button on the keyboard, but sill no luck Im typing this message on my sista's laptop.

Can someone pleae help thanks