it should be in the market place but if it isnt just ask a friend to install it into your hard drive
then you can play the broken disk
In addition to the pervious post you could also go to a shop that sells games such as gamestop which might have a game disc repair machine. i got my copy of BO repaired for about $3.00. The game isn't in the XBL marketplace yet, but it should be added about halfway into the games lifecycle.
yep, you can even buy cheap manual buffers for about a £1. They work by polishing of the top layer of plastic so you have to be carefull when using the shop machine one's because your disks get thinner and thinner
If you wanted to buy it from Xbox you would get charged a brand new 60 bucks for the game .
Problem is the game isnt available for online purchase yet and probably wont be for at least a year.
Have you tried copying it to the hard drive first ?