Scratched Leopard Disk.

I purchased the family pack and I have Leopard Installed on all Macs except for one. a 1Ghz iBook. When I placed the DVD in the iBook I started hearing scratching sounds. I took the DVD as fast as I can out of the system but it was to late there is a circular ring around the DVD near the Top...

So the questions.

1. Is there a good way to fix this scratch.

2. Can I go to the Apple store and get the CD Replaced at cost of the Media Say under $20?

The iBook is the least used system. I just wanted leopard on all of them.