Why will some CDs not load/be recognized by my MacBook Pro

Hi,

I've bought a pair of Windows 7 Professional installation discs (32 & 64-bit versions). Following the instructions for Bootcamp, the discs will not be recognized by my Mac and refuse to be ejected. I tried loading them on my friends Macbook Pro which he recently bought and they work fine. I tried see if they would load on a PC and they do so I have excluded any faults with the CDs.

I therefor presume there must be something wrong with my CD drive, but for the most part, it recognizes discs, both Mac and Windows specific.

Why does it not recognize these discs, is it due to dust in the drive or something else that maybe I can correctify. Unfortunately, the Mac is out of warranty. It is a Macbook pro 15 inch mid 2009 unibody.