Remove Public folders from old Exchange 2003 server after Exchange 2010 transition

If you can't remove public folder database on your old Exchange 2003 server (and after having replicate correctly data to Exchange 2010)

You can try this :

ADSI Edit >
Configuration
+ CN=Configuration
+ CN=Services
+ CN=Microsoft Exchange
+ CN=YOUR ORGANISATION
+ CN=Administrative Groups
+ CN=First Administrative Group
+ CN=Servers
+ CN=SERVER NAME
+ CN=InformationStore

Delete manually and dismounted the store.

You are able to uninstall Exchange 2003.