iCow, welcome to the forum! I've had this very same thing happen to me, when I downloaded Windows install discs from TechNet. It only happened a couple of times, and I don't know why it did. When I reburned the discs, it installed fine.
My optical drive is a DVD-ROM (IDE) as yours is. I don't know if it's looking for a SATA DVD-ROM or not.
But what you can do, if you have access to another computer, is simply download another disc, it's free and legal. Just make sure that it's the same DVD (Windows 7 Home Premium 64 bit).
You can download a replacement disc at:
http://msft-dnl.digitalrivercontent..../X15.65733.iso
It is the same disc as the one you have, and should work. It's a 3GB download, so once you have it, burn it slow with your favorite software. I use both ImgBurn & XPBurnerCD, they both do good, just burn the file slow.
PS: If my link gives problems, just search X15.65733, it should be the first or second link down.
Best of Luck,
Cat