It's a custom script made with Prototype. It would be fairly easy to do, as all it is really is an absolutely positioned DIV that is toggled on and off, with a bit of fading thrown in. jQuery would make this a piece of cake. At its simplest:
If you look at the documentation, you'll see that you could also make the fadeout transition different.
As for the code, it doesn't looks particularly more bloated than a lot of sites these days. What do you mean?