Active directory asp.net in directory

I would like to be able to log into a web page using a valid active directory name and password.

username and password are entered in the text boxes. if they are correct, I would like to redirect to another page.

how it can be coded.

in the second task

after executing any code, log in as administrator using the code and open an account.

I've heard it is called impersonation.

how can i accomplish the above?

I am using visual web developer 2008 and vb.net

thanks!