Mac OS X 10.6: Deleting a keychain
If your keychain has become inaccessible for some reason (for example, if you’ve forgotten the password), you can delete it and create a new keychain.
To delete a keychain:
Open Keychain Access, located in the Utilities folder in the Applications folder.
If keychains are hidden, choose View > Show Keychains.
Select a keychain in the Keychains list.
Choose File > Delete Keychain (keychain name).
If you want to delete the files related to this keychain click Delete References and Files, otherwise click Delete References.
If you remember your password later, you can recover the items stored in the keychain by choosing Edit > Keychain List and adding the keychain file.