Take a look here.
You want to read the Installation guide a few times just to get an idea on what's involved.
Installation Guide
Boot Camp 4.0 FAQ
Windows 7 FAQ
Basically you have Boot Camp Assistant (on the Mac) start everything off and it will partition the drive to the size you want and ask if you want to download the Windows support files, then it will let the Windows 7 (or XP if 10.6) disk boot into the Windows installer and then you have to format it NTFS, it will then install Windows onto the partition you made earlier and reboot into Windows and then you insert the Boot Camp drivers to install into Windows.