if your thinking about getting Vista but are not sure about performance or compatibility .. keep your XP .. but .. just make it look like vista 
http://www.crystalxp.net/galerie/en.id.130.htm
for a simple 27.64MB download it will completely change the look of your XP
you will have the new menu bar look, new icons, new sounds, new loading screens, even the rocketdock.
im currently using it on my system and its great. the sleek look of vista BUT the performance and compatibility of XP .. you can also modify what you want to run (turn on/off rocketdock, turn on/off shaders etc)

http://www.crystalxp.net/galerie/en.id.130.htm
for a simple 27.64MB download it will completely change the look of your XP

you will have the new menu bar look, new icons, new sounds, new loading screens, even the rocketdock.
im currently using it on my system and its great. the sleek look of vista BUT the performance and compatibility of XP .. you can also modify what you want to run (turn on/off rocketdock, turn on/off shaders etc)