Why would "Drop Database" fail on local SQL Server 2005 Express instance?
Depending on whether or not these are subscriptions or the published database you are going to need to drop the replication data. 

MS Published a handy doc with example scripts here http://support.microsoft.com/kb/324401

This one is a general tool to clear out what you need

sp_removedbreplication '&lt;Database name&gt;'