Andy
OK, your heading for trouble.
If you are sure you really want to do this, you need to dive into it and
learn where all of the many pitfalls are. If you are looking for something
that is free, this also means that whatever way you choose to do this,
there probably will not be any support if things go wrong.
Take a look at the following website to get started.
XP's Luna theme for Vista by ~Shifty102 on deviantART:
http://shifty102.deviantart.com/art/XP-s-Luna-theme-for-Vista-58027692
--
Ronnie Vernon
Microsoft MVP
Windows Shell/User