Hello and Welcome to Free PC Help James.
As Maynard and Randy have already asked, how much RAM do you have? Vista uses a tremendous amount of RAM to operate smoothly and seeing you have no ordinary version of it, I think the demands would be comparatively higher. Another thing is that were you using XP before. Because if you started experiencing problems after an upgrade, then I think you have put your finger on the problem. In that case, I would recommend you to downgrade to XP or upgrade your system. Please clarify the needed details.
-- Goku