Macs without the Superdrive give you the additional choice of creating a bootable USB thumb drive from an ISO.

If you want to (or can) install Windows using your Setup-DVD, just pop it in and hit "Continue".

If you'd rather install Windows using a USB thumb drive, read the steps below first and then move on. At any rate, make sure that "Download the Windows support software for this Mac" is checked, which starts a download assistant that puts the Boot Camp 4.0 drivers on your desktop, on a separate USB drive or burns it onto a blank CD/DVD.

On the next screen, you're going to face a tough choice: How much disk space do you really need for each operating system?

Windows needs at least 20GB to work properly (system files, page file, hibernation file, system restore points, etc.). This is the absolute minimum. Depending on how much data you want to carry around with you and how many programs you need, you'll likely need a lot more than that.