ok, when you use msn messenger for the first time in windows xp, it brings up that special dialogue, asking you to put in your msn address etc and it contacts the msn server.. it then has a little checkbox saying somewhere alone the line (in the setup wizard) "click here to associate this account with windows". just check off that and it won't be associated with windows
sorry for this rough description, as i haven't had to do this for ages but i know you can do it
if you need more help just PM me