Bootcamp Installation Problem

I get this warning when I try to install Windows 7 Home Premium on my iMac using Bootcamp Assistant. I went through the whole setup and installation guide, but to no avail. I have successfully gone through all steps in the process, including partitioning the disk. This error comes up on the first stage of the setup.

The full error message is:

A required CD/DVD drive device driver is missing. If you have a floppy disk, CD, DVD, or USB flash drive, please insert it now.

Note: If the Windows installation media is in the CD/DVD drive, you can safely remove it for this step.

I have the original disk for my system, but I can't insert it in the middle of the process. I think I need the drivers to install Windows 7, but I can't install the drive until Windows 7 is installed.