user name in database!

Hi,
I'm wondering how to do this, I'm working on the on a datagrid and I'm
using windows authentication. I managed to get username on to a login
form, but I want it to be stored into the database.The code of web
config looks like:
authentication mode="Windows"
identity impersonate="true"
And the Login page looks like on(Page_load):
Response.Write(Page.User.Identity.Name);
Thanks.

.