Well, the centering is just a simple CSS style declaration. You may have to fiddle with the positioning, but if you open the template file "login.tpl" you can see what div that is. Then just find the div in the css file and modify it. I'm not 100% sure of the exact items; however, they aren't that difficult to figure out.
You'd have to dig into the code to find how to change the title and the logo text. I don't have the source in front of me, but if you just search for it, it will come up (possibly in a language file).