How to make Url Blocker in C# .Net 4.0 Desktop Application

Question

Hi Everyone...

I want to make a software like Url Blocker , means by that software one can block any website in Mozilla  or Chrome or Internet Explorer or in any web browser.

I found host file in this location "C:\Windows\System32\drivers\etc\hosts"

but this host file can be modified only in windows XP , it can't be modified
in Windows 7 , then what to do ?

and one more things is that this host file is only for Internet Explorer only
not for other browsers .

so please give me some solution ...

Thanking You