vista kai kaaran slow bhayeko bhanna mildaina, computer ko hardware specs ma bhar parchha slow ra fast bhanne kura.
comparatively xp (sp 1-3 je haale pani ) vista bhanda ali chaado chahi pakka chalchha
and i prefer xp, kinabhane saya ota seurity message xp ma aaunna.

go here for free download of xp: http://www.filedownloadfull.com/2008/11/microsoft-windows-xp-pro-sp3-november.html

and then install it.

good luck