populating a dropdown from database using javascript webservice

Error    1    The type or namespace name 'List' could not be found (are you missing a using directive or an assembly reference?)   

one more thing i would really like to know

whts the difference in terms of working, processing & speed when used with webservice & normal aspx.cs page

i mean currenlty i have the dropdown populated in my aspx.cs page

as the normal asp.net code

so if the same code is put in webservice than how differnt it would be

You need to add the following namespace

using System.Collections.Generic;

There's no difference in performance

Error    3    An object reference is required for the nonstatic field, method, or property '_Default.conn'  

i have used connection string as i need to get from databse so i get the error

secondaly as u said there is no difference at all in using the code in webmethod & our normal code than why do we need to use webmethod

currently i do have a code on server side to popullated dropdown

but only thing is that there is postback which is clrealy visible as it takes long time to populate teh dropdown

1. You need to intialize the connection object

2. AJAX call can be made only to web methods and not to normal methods

conn = new SqlConnection();         conn.ConnectionString = constr;         conn.Open();

1)connection object initalized

2) u mean by using the web service & populating from javascript I can avoid postback & populate it fro client side which cannot be done with normal methods?