Exchange Server 2000 convert to Native m

I would like to change our exchange server 2000 to native mode, but an old 5.5 server that is no longer in existence shows up greyed-out in the Exchange System Manager snap-in. This apparently prevents the upgrade to native mode. MS claims you must remove the final 5.5 server from the 2000 site using Exchange Administrator on the 5.5 server itself, but how can you do that when the 5.5 server no longer exists!! Any tips? Thanks!...