There are many transformation packs available which will convert XP’s look & feel to Vista. The one I use is Vista Inspirant, which completely changes look & feel. It also changes startup & shut down tones with a pleasant sound.
Another popular transformation pack available is Vista Tranformation Pack.This pack alsoDoes everything that Vista Inspirant do. Additionally it also features 3D flip which can also be installed Manually .
There are lot of other packs to change XP’s look & feel. Not only to look like Vista, but also other OS like Linux KDE & Mac.
Here Some Other Links :-