Security :: Fetch A Page From A Remote Php Web Appln In A Different Domain?

I am trying to fetch a page from a remote php web appln in a different domain. The page contains a chart image which I need to display in my web app. The chart image is dynamically generated using jquery.
Now the remote web app needs to authenticate myself as user i.e username of my machine. So the first time I made a request for its first page it asked for my username and password in the browser ( I.E). From next time it doesn't ask for my username and password and opens the first page.My username was added to the user DB and probably it stores my IP or computer name.Then the chart page also opens in the browser(I.E).
After some time if I try to open the chart page it comes up with some messages and junk values.
But if I again open the first page and then the chart page in the browser it opens up with the proper chart image. So everytime I need to access the chart image I need to authenticate first by opening the first page since the session timeout for authentication is not known. The above process which was happening in browser has to be replicated in my code (C#) in my web app. Now for authenticating myself i.e myusername to the remote appln I write the code below but all I get is some messages and junk values. so how do I authenticate and then access this chart page.

[Code]....