Windows 7 x64, SQL Express 2008 - Problems attach Northwind database

Hi, I've attached Northwind many times before, but seem to be unable to do so in Windows 7. I tried attaching from Visual Studio, using osql, and finally (after many hours) installed SQL Express 2008 / SQL Management Express 2008. All methods failed. The last failure (using SME 2008 Attach Databases) is sometimes:Unable to open the physical file "C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\DATA\northwnd.mdf". Operating system error 2: "2(failed to retrieve text for this error. Reason: 15105)". (.Net SqlClient Data Provider)and other times: Database 'Northwind' cannot be upgraded because it is read-only or has read-only files. Make the database or files writeable, and rerun recovery. (Microsoft SQL Server, Error: 3415)I have, of course, verified countless times that the files are N ...