it depends
Go onto multiplayer which will take you to a random free-roam lobby. then, bring up the menu which has the games list and the players list on the lobby. dgo down the page on the games list and click on undead overrun.
it would depend how badly the disc is sratched or damaged if you take it to your local game shop they should be able to clean it for a low cost!
about 12-24 hours -[pm] Nightmare
it takes 1 hour to download
well when you download it, its pretty quick.
3 sec
zombies like to eat brains so if you take out ur brain u can feed them.... u can also substotute with raw cauliflower! :)
a long time
A really long time
Not to long as soon as you download it
It will depend on your download speed. If you have a 30mb/s download speed it will take 2 seconds. If you have a 512kb/s download speed it will take 2 minutes