Admin CP > Styles and templates
Theres a little box at the bottom (like a button) "create new style" click that.
Then name it something like "TEST 1" then reload the Admin CP then go to Styles and Templates, one the test skin it should say (in like a drop down menu) "All style options" click the button next to it, scroll down a bit till it has loads of little text box's on the right... Normally saying...
"Images/Statusicon"
"Images/... etc"
Rename all the "images" bit to "Test" then redownload vBulletin.
Once you have redownloaded vbulletine xtract it and go into the "Upload/Images" folder, edit all the images you wish then rename the folder "upload/images" to "upload/Test" and then upload it to your forum dir.
(Normally public_html/forum) and then edit from there

.
Sorry it's brief but uno .
Jac