Well it took all day because of my noobish skills in HTML and CSS, and trying to get it right, but I got ECC's welcome block done.
Using the PHP Conditionals plugin, I was able to make this show up only for guests, which is the point of it. It has a brief message and two buttons so far, one for the normal way of registering, and the other for the two-click Twitter registration or one-click log-in.
Here's a little screenshot for you:
Says it pretty clearly if I do say so myself :)
Hopefully it will be attractive enough for guests to click one of the buttons. It's also displayed globally, so there's no way to hide it.