1. Open SQL Management Studio Express and log in to the server to which you want to attach the database.
2. In the 'Object Explorer' window, right-click on the 'Databases' folder and select 'Attach...' The 'Attach Databases' window will open.
3. Inside that window click 'Add...' and then navigate to your .MDF file and click 'OK'.
4. Click 'OK' once more to finish attaching the database and you are done.
The database should be available for use.
NOTE: Pleate take a backup of the *.mdf file before you import. This is because, if you import an MDF file from SQL Server 2000 into SQL Server 2005, for example. There is no way you can reattach the file to the earlier version of SQL Server.
