how can i connect my asp.net - C# form with sql server 2005 database?

Well, as a beginner, you can try the code below which fetches some data into a dataset.

string strCon = @"Data Source=yourservername;" +
"Initial Catalog=Northwind;Integrated Security=SSPI";

string strSql="select * from customers";
SqlConnection con=new SqlConnection(strCon);
con.Open();

SqlDataAdapter dadapter=new SqlDataAdapter();
dadapter.SelectCommand=new SqlCommand(strSql,con);

DataSet dset=new DataSet();
dadapter.Fill(dset);

con.Close();


Regards
Mike