Setting default keys

We have recently upgraded to PGP desktop 10 from PGP 8 and are setting up our keyrings, I have been given the task of setting the new system up

the default key on the keyring is set to our individual key(from our username)  , but we need to set the default key to be a shared key from the server

How do we set default keys on the keyring?  Is there any way to do this ?

thanks in advance

Neil