They plug into the regular power points, like what your CD-ROM drive uses. Most of them have a female and male adapter so that you don't lose connectors.
And thanks, Yeah, I don't have anything to really put in there. I might someday, but right now the computer does what I need it to do, I'm happy.
If I start doing anything it will be the appearance and cooling. I want a good heatsink/fan. A couple more 80MM fans, I think have room for four more 80mm fans.