As I’ve explained before, I’m not on the Vista bandwagon and will only get there when someone extricates XP from my lifeless fingers. The only feature I can actually appreciate from Vista isn’t a functional one, it’s the appearance and the graphical interface changes. Shiny isn’t enough to make me switch operating systems, but it is enough to make me look into changing the way Windows XP looks. There are a few add-ons that can make Windows XP look more like Vista but still keep the speed of your system up to par.
The best add-on packs I have found for XP are called BricoPacks. They are free and will give your WindowXP system an entirely new face. They do this by replacing system files with modified versions to make your system respond differently. While they do warn of some system incompatibilities with certain software, I haven’t run into any with their latest release and removal was clean.
CrystalXP is the site that offers the different Bricopacks for download. There are several different packs designed to give your system different appearances. For the Vista look, you’ll want Vista Inspirat Ultimate 2. After installing, your system will look like this.

Since these modify your system files, there is a risk of problems, but I’ve had these running on two systems without any problems. Earlier versions had problems with some windows apps, but later versions have worked this out.
These bricopacks are where I discovered the OSX style dock for Windows XP.