Flash is rather limited... and what you're suggesting is a shell that uses (local or www) Internet-based applications.

I'd imagine you could make a "window" that uses a default browser to access the internet, but you'd have to look into that yourself.

As for Messenger, you'd have to use an online messenger suck as Meebo or ILoveIM... sadly the MSN Web Messenger is no longer online, as it was intergrated into Hotmail.