Mirroring only a section of an object

This seams really difficult but all I want to do is take the hands of my character and mirror it on a y axes because I put the thumb on the wrong side of the hand. As far as I can tell there is no way to do it with the edit tools provided in blender.

It looks like all I can do is duplicate the object, crop it down to just that part, translate it to a negative y then join it again. In contrast in light wave all you would do is select the surfaces and hit CTR+V (I think, been a while), place your line and hit enter.

So is there an easy way to do this?

Go to object mode, use shift-s, snap cursor to selection (with the object selected).

Go into edit mode, pick the 3d cursor as the pivot point (you can hit period for that), select stuff, and shift-d, S, -1, X-or-whatever-axis.

That at least cuts the extra object creation out of it.

You could also use shift-d in edit mode, escape, p, to sepearte a duplicate into another object faster.

alright cool thanks