How to simulate a button click action with keyword in a textbox to get httpresponse result?

Hi,
I wonder how can I do this in asp.net:
For some sites there are search function and allows user to search by certain keyword like city or zip code, once you type in the keyword and hit search button, it returns you the search result.
What I want to know is how do I (in my code) mock up that I input a keyword and hit the Search button and receive the httpresponse? I need to get the httpresponse and do my analysis.

Thank you very much.