Just like for Textbox you get the txt using textbox1.Text, for combobox, you need to get the selectedindex and then get the text
Try this..
private void button1_Click(object sender, EventArgs e)
{
string s = "";
if(comboBox1.SelectedIndex>=0)
s = comboBox1.Items[comboBox1.SelectedIndex].ToString();
SqlConnection con = new SqlConnection();
con.ConnectionString = @"Data Source=.\SQLEXPRESS;AttachDbFilename=c:\documents and settings\aquib\my documents\visual studio 2010\Projects\login\login\Database1.mdf;Integrated Security=True;User Instance=True";
string q="insert into Table1 values('"+textBox1.Text+"','"+textBox2.Text+"','"+s+"')";
con.Open();
SqlCommand cmd = new SqlCommand(q, con);
cmd.ExecuteNonQuery();
con.Close();
MessageBox.Show("suceed");
}
Here I replaced the last parameter with combox selected item.
Hope this helps.
cheers