How to use Proxy/ Hiding IP of HttpWebRequest ?

Question

I am developing Windows Application and using HttpWebRequest. My requirement is, While sending a request to a URL, I want to hide my IP address, or I want that the requested URL gets some other IP from My request. Can anybody suggest how to do this? Actually, I am developing an Web application and doing this to post in a web site. In our Web- application, we are using post to fill up forms. I want that my httpwebrequest should go through other proxy to the main server. e.g. Providing proxy Support to the application. The application will use some other proxy. My request will to the server through that mentioned proxy so IP of Proxy will go to the Main requesting server and originating PC's IP will be hidden. How this can be done? Please help, if any one has sample code for this then please give it. Any hint will also be fine. Thanks & Rgds, Kiran Suthar.