As far as I know, on BizTalk 2006 you need this:
– Copy the dll into the Pipeline Components folder in your BizTalk installation folder (as in 2004) on your development machine. This is required so that Visual Studio recognizes it and shows it on the Toolbox in the Pipeline designer
– Deploy the dll into the GAC for real server deployment. This is the change from 2004, where it was not recommended. Instead on 2006 the recommended practice is to deploy pipeline components to the GAC for server installation.