During the installation process, I get a message that pops up that says to "Please insert the disk: Windows OEM Preinstallation Kit CD".
You downloaded the OPK image, burnt it to a DVD, started the installation and soon got that message, correct? If you have several dvd drives in your system, you may want to insert the disk into a different one. Maybe also, verify that you downloaded the right image.
Or try this way: insert the opk disk, wait, right-click on it in the explorer, from the context menu choose install/autorun (whatever appears). A chance you are running the installation from the wrong executable.