Yes...you will be able install and update and use XP normally. Now this is were it becomes tricky. If there are any other vulnerabilities discovered, MS will no longer create fixes for it. So you will be using it like an "as is" product or "at your own risk" type of deal. IMO, is just a ploy to get one to buy the next OS. I know a lot of people that have and still use windows 98/98 SE and use the web and not had any ill effects. Me personally, I have 2 XP machines that I will continue to use.
Yeah it can still be updated and all, it just wont be supported.
the only issue I am seeing is people are panic downloading right now as they are trying to squeeze every last update in.
I can tell as my old laptop that came with XP is taking forever to install any update