First things first: I don't appreciate software piracy and I really want to spend money on software that I use and that I work and make money with. I don't want this question closed just because I consider downloading software, I only want honest opinions and alternatives.

Here we go: So I have my OS X Snow Leopard Upgrade DVD, but it's horribly scratched and won't boot anymore. It endlessly loads and at some point I have to force pull it out of the disc slot.

How can I reset my Mac then?

• Can I take my original disk to an Apple Store and ask them for a replacement? Will they believe me, even if I don't have the receipt anymore?
• Would owning the original disk make it okay for me to look somewhere on the internet and download it? I don't even know if that will work without hassles.
• Could I try to read the disk to an image with some error correction methods? Maybe during boot it can't read some files, but some other program can?
• Is there any other way of resetting the Mac? Mine's now over 3 years old an I seem to have misplaced my original discs that had 10.4 on it.
• Or should I just buy a new 10.6 upgrade disk? (Which is not really what I want to do)

Answers and opinions would be much appreciated.