The Wow is here! (With some tweaking)
I just came across a great site called MyVistaBoot.com . As the name suggests, it is dedicated to sprucing up that fairly boring Vista boot screen. Each new boot screen is packaged with an installer so it is trivial to get them on your system without resorting to the use of third party applications as was necessary with Windows XP. Take a look, there are some very elegant ones on there to suit every taste.
UPDATE: My mistake, the file downloaded replaces the winload.exe.mui file directly. It is not as simple as just replacing the Windows file but the instructions are clear and concise.