|Wel It's definitely compatible with Windows 7 so that's not the problem. The CD must be damaged/scratched. To download the game without paying isn't possible unless you get a pirate version which we do not encourage at all.|
To download it legally for free from the developer you would have to prove to them that you already bought a copy with a legitimate serial number.
I remember a company sending me a driver disc for my motherboard a while back. The PC wouldn't read it so I made a "disc-to-disc" copy of it using Nero's "Copy CD". My PC was able to read and install from the copy no problem.
You might want to try that.