Polysmoothing
 

theres a feature in 3dsmax called NURMS surfaces and what it allows u to do is have a low res poly object, then u activate NURMS and the surface now becomes a cage and uhave a high res model inside the cage.
if u edit the cage u will also modify the high res model, but whats good about it is u can switch nurms on and off whilst making tweaks and those tweaks wud still remain intact. if you had a polysurface and u just smoothed it, u wud have to constantly undo to go back to the unsmoothed model, and by doing so, any changes u make to the high res u will have undone.

i hope that was easy to understand, im just looking for sumthing that will do what i said above

Maya 4.5 has a Smooth Proxy function that does that I believe.

Polygons->Smooth Proxy>

SubDs as well.