C# HTML/PHP POST Help

Hi,
       My problem is:

I have a webpage, with 1 text field, and 1 submit button.
I need to enter a URL into the text field, and press the Submit button, all from a C# program.
After the submit button is pressed, the webpage will download the file you input (the url), And i need the program to download the file.

Webpage info:
[Form: action = "site.com/process.php"  method = "POST"  name = "dl"]
[TextField: input name = "download"  type = "text"]
[Button: value = "Download"  type = "submit]

 
I have been playing around with this for a very long time,  I would greatly appreciate any help.

Thanks in advance,
Kyle.