Second, what do you know about C++? Not anyone can jump into such a complex project such as an IM client which I am hoping will has some kind of GUI, which requires learning Windows API to make basic forms, dialogs and etc. then you have the networking side of the client and not to mention server if you make the im client your own or using an exiting IM service out there like aim, yahoo, kind of how pidgin works. for that youll need to know the networking side of C++, which is winsock or boost asio's networking lib, etc.
To be honest with a post, you sound like a young kid in way over his head.
jesus, you know how to make a form, yeah because thats the easiest win32 api code to copy.
Win32 is hell. GTK/Qt or even better, WxWidgets are a bit easier. But if you really want to go the MS route, you could whip up an interface much more easialy with MFC (Especially with Appwizard. And the Internet Controls would come in handy)
I think there is an IM libary called libpurple. thats what a lot of major Opensource IM clients use.