Desktop Application that manipulates webpages

Question

Hi, I will be short and concise, I need some guidance:

I want to create desktop application that will connect to a user account through the web, or maybe it should implement the web browser itself, just with + functionality (manipulating the browser inside the desktop application), that will be able to click on Hyperlinks (images or just plain text), that will be able to write what I tell it to write in a textbox, and to click the submit button after that. That's what I need. 

The application should work without the mouse at the moment that it is on.. It should work by itself. 
I think that this can be done in 2 ways as I see it.
1) To manipulate the DOM tree. 
2) Just to manipulate the different objects like Hyperlinks and text areas as graphical elements? 

I am curious to know if I can work in VS 2008, C# and not just work with Internet Explorer? Maybe Chrome, or Firefox? Is that possible? 

What I want, is for people to tell me, is that very hard to do? What should I know,, where should I go, since now,, I'm just stuck at the beginning ) Maybe it's not even possible? 

The site that I'm talking about, that I need to connect to, is a (RIA) and it uses Ajax heavily, so parts of the webpage is updated constantly.. Hope this helps? 

Thank you for your time in advance,, if you need other information, I will be glad to tell you more.