After the installation I could still not open DTS packages. I got a error like
SQL Server 2000 DTS Designer components are required to edit DTS packages. Install the special Web download, "SQL Server 2000 DTS Designer Components" to use this feature. (Microsoft.SqlServer.DtsObjectExplorerUI)
A quick search gave me the thread "SQL Server 2000 DTS Designer components are required to edit DTS packages - in SQL 2008". I changed the environmental variable as described where I put the value for DTS before anything from SQL Server 2008 and Visual Studio.
The thread is saying that restarting Management Studio is enough to get the new setting, but I had to restart the workstation. Perhaps as I am not local administrator with the my normal user.
Reference
MSDN Library: "Support for SQL Server 2000 DTS in SQL Server 2008 R2"SQL Server Forums: "SQL Server 2000 DTS Designer components are required to edit DTS packages - in SQL 2008"