is it possible to take a turbo from a 900SE and put it in a 900S?

It should be. As long as they have the same kind of engine (most likely a 2.3L I-4), which they ought to, the turbocharger should be interchangeable. The 900 SE was just a higher trim level, i.e., wooden dashboard inserts, leather, etc.

go to saabcentral forums and ask around, im not sure if they used the same internal components in both models.