Have you made sure that you have uploaded the cpstyles? Or that the permissions are correct for the folder and the subfolders within it? Look at the source code on a page in your admin cp, around the fourth line is something like this:
HTML Code:
<link rel="stylesheet" type="text/css" href="../cpstyles/vBulletin_3_Frontend/controlpanel.css" />
Point your browser to it and see if it comes up. If it doesn't come up in your browser, the either is doesn't exist (so upload it) or the permissions are incorrect (so fix them).