If JavaScript is off, what user will see?
If steps are made with usual javascript tabs, then (only if tabs are made with a graceful degradation in mind) user will see one very long form (which isn't so user friendly).
But if it's ajax tabs (based on 5 real pages), then if JS is off user will see 5 links to five pages. Which is better, also, because you can press "back" and refill something you changed your mind about.
Generally, I believe that 5 separate pages, with links "previous" and "next", so user can leave the form not filled up to the end and come back to afterward is a best option. Perhaps some smart ajaxifying could make it somewhat easier, but only with a great thoought behind it.