Problem With WPF Application And SQL Server Database

I made an application with animations in WPF with Visual Studio 2008 Team System and SQL Server 2005.

So I have Windows XP and Windows 7, in Windows XP that I have Visual Studio and SQL Server and Framework 3.5 it works very well, but in Windows 7 and in other computers it can not connect to database, first I thought it's about Framework but in other computers I have this problem again.

My connection string is:

con.ConnectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename=\"|DataDirectory|safedb.mdf\";Integrated Security=True;Connect Timeout=30;User Instance=True";

What do you think? I must install Visual Studio in every computer?

What is the problem?

this is the code of that button which has error in another computer that doesn't have Visual Studio :

            login l = new login();
        DataSet ds = new DataSet();
        SqlConnection con = new SqlConnection();
        con.ConnectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename=\"|DataDirectory|safedb.mdf\";Integrated Security=True;Connect Timeout=30;User Instance=True";
        con.Open();
        String sql = "EXEC GetLoginModel";
        SqlDataAdapter da = new SqlDataAdapter(sql, con);
        da.Fill(ds);
        bool n = (bool)ds.Tables[0].Rows[0].ItemArray[0];
        bool s = (bool)ds.Tables[0].Rows[0].ItemArray[1];
        l.radioButton1.IsEnabled = n;
        l.radioButton2.IsEnabled = s;
        con.Close();
        this.Close();
        l.Show();

yes I knew but i thought we need this program only when we want to make databases not using it ...

i saw a lot of softwares that they work with mssql but they are tiny and they don't need any other program to install ???

so what ?

and please give me the link of sql server express edition only for using with my app ...

it means i must place that besides of my app ???

Thanks A Lot Again My Sweet Friend :X