Uninstall Half Installed Vista To Reinstall

My friends XP crashed so I leant them my recovery disc (my old pc had XP this one has vista), when the xp recovery disc didn't work for them, they used my Acer Vista one which has half or more loaded vista and stalled probably because the lap top is to old to handle it. Anyway there is a blue Acer loading screen doing nothing and the vista programs run behind it which makes it difficult to see what you're doing. They brought it around to me as I can use this pc to see what I'm doing and try and fix there's more or less by feel, if that makes sense. They tried reinstalling my xp disc but vista seems to super seed it and it wont take, which doesn't surprise me.