How to access a 3rd party website Programmatically using HttpWebRequest?

Question

How to access a 3rd party website Programmatically using HttpWebRequest? 1)From my website i want to write code to login to another website using Login Id and password 2)Then After logging in i need to goto another page by clicking on a ling or button. 3)Then in the resulting webpage i need to update my personal info like password in a textbox and save it using save button. Everything must be done programmatically invisibly ie without displaying the webpages. Please can anyone help me by providing a working sample code simulating my problem.

Will the Sessions and Cookies from 3rd part website will be a Problem?