You need to attach the database rather than perform a restore. 

Using Enterprise Manager:

Expand the registered SQL server

Right-click Databases, select All Tasks -> Attach Database…

Click the “…” button to browse for the .mdf file

Highlight the necessary .mdf file and click OK

Click OK again

The database will now show up in Enterprise Manager

To use Transact-SQL, use the Query Analyzer tool:

Here is sample command based on your files above. You will need to specify the correct directory where these files exist. The example has the files in the C:\SQL directory.

EXEC sp_attach_db @dbname = N’rs_ds’,    
 @filename1 = N’C:\SQL\rs_ds_dat1.mdf’, 
 @filename2 = N’C:\SQL\rs_ds_dat3.ndf’,
 @filename3 = N’C:\SQL\rs_ds_dat4.ndf’,
 @filename4 = N’C:\SQL\rs_ds_dat2.ldf’