Q:

Transfer a database to SQL Server 2008 from SQL Server 2008 Express

Anyone know the generic practices transfer the database to SQL Server 2008 from SQL Server 2008 Express (I'm not sure it is r2), when I try to attach the .mdf file from Express, there is an error message.  

the database cannot be opened because it is version 661.  This server supports version 655 and earlier.  A downgrade path is not
  supported. 

A:

Well, the message is clear: the file you're trying to attach from Express is from a newer version of SQL Server
So it appears that you indeed have SQL Server 2008 R2 Express, and you cannot attach this to a SQL Server 2008 instance.  There's no way, no hack, no workaround, no trick, or no third-party tool to achieve this - it just cannot be done - period. 
So you either need to upgrade your main instance to SQL Server 2008 R2, too - or you need to find another way (like scripting out the structure and/or data into .SQL files) to move your changes from one instance to the other - or use a third-party tool like Red-Gate SQL Compare to synchronize the changes between the two instances.