The Dark Age of Camelot Gold Edition contains in the packaging two cds and one cd key.
The software contained on the cds is the Shrouded Isles version of Dark Age of Camelot along with the Foundations expansion. The classic Dark Age of Camelot Client is not included in this package, it is just one client (Shrouded Isles) spread across two cds.
The key provided can be used to do only one of two things.
It can be used to either:
1. Create a brand new account with classic and Shrouded Isles access (click 'Create New Account' at login screen and enter the cd key at the bottom of it)
2. Upgrade an existing classic account with Shrouded Isles access (log in using your username and password after installing the software, and at the server selection screen click 'Activate Expansion' and enter the cd key in here)
Please note that once a key is used it cannot be used again, nor can it be de-activated. It is permanently attached to the account it opens or upgrades.