It depends which model of Stepwagon you have. If, like me you have either an RF1 or RF2 (mine's a 1998 S reg) you had the choice of either the Pop-up seat model or the Turnaround model.
I've got the Pop-up one and the middle seats don't rotate - it's a bench seat that is split equally down the middle. For each half of the bench you can fold the backrest forward to create a table then twist the circular knob to fold each half of the seat forwards. But that's all they do.
The Turnaround models have a 65/35 split where the large side near the window is a two person seat and the seat near the door is small and folds up. Have a look at this classified ad on eBay to see what I mean
http://cgi.ebay.co.uk/Honda-Stepwagon_W ... 19b78b84c3. You can see in the interior pics that the seat nearest the sliding door is noticeably smaller than the others. It's only the bigger 65% of this seat that rotates, the small seat stays folded up.
My handbook (available from the Club Shop for £20 and very useful) tells you how to rotate this seat - it looks easy to do but it's quite difficult to explain without the accompanying diagrams. I can scan it in and email it to you if you want