怎样用C#2005编写一个SQL server 2000数据库连接类 并调用这个类

举一个简单的例子:
public class DBOperate
{
static SqlConnection sqlConnection=new SqlConnection

(System.Configuration.ConfigurationSettings.AppSettings["ConnectionString"]);

public DBOperate()
{

}

//执行SQL语句,如Select
public static DataTable Select(string sql)
{
try
{
SqlDataAdapter sqlAdapter1 = new SqlDataAdapter(sql,

sqlConnection);
DataSet returns = new DataSet();
sqlAdapter1.Fill(returns);
return returns.Tables[0];
}
catch (Exception ex)
{
throw (ex);
}
finally
{
sqlConnection.Close();
}
}

//执行SQL语句，如UPDATE，INSERT等
public static void ExcSQL(string sql)
{
try
{
SqlCommand sqlCmd =new SqlCommand(sql,sqlConnection);
//if(sqlConnection.State.ToString() == "closed")
sqlConnect