Now you can use your DataSet ds.
if you use indexes like table 0 and row 0:
string user = ds.Tables[0].Rows[0];
string pass = ds.Tables[0].Rows[1];
or you can use names of the tables and rows:
string user = ds.Tables["MyTableName"].Rows["Username"];
string pass = ds.Tables["MyTableName"].Rows["Password"];
Good luck,
Edo
* Note that you missed closing the connection, [cs.Close();]