Xp ? vista? (DX 10)

seeing as this computer im getting comes with a clean drive and i own both xp and vista already ,which is best ? i mean hate vista and use xp, but i seen alot of stuff about dx10 and vista? can you run dx10 with xp? and or good on xp? i have no clue about this new stuff lol help me out plz

and by clustered I meant cluttered, my bad.