Of course not. If like most people you're using a router (and I really hope you are) that's only the external IP the router shows the world, not the actual, protected IP of the machine behind the router you're trying to connect to. So in effect, you're only connecting to the router, it won't allow you past it. That's why routers add security.

You need to run ipconfig on the machine you want to connect to and get it's IP. Then setup the router to foward that IP. You also need to open port 5900 as it should be closed by default. Actually, I'd setup VNC to use a slightly different port, say 5905 or 5925, something a little off the default 5900 just to help throw off simple script kiddies.