Centering multiple objects and scaling for fbx export.

Does anybody know how to center an ungrouped set of objects?
Example, select several objects of which none are grouped or parented.
Then, center them on the x,y,z grid according to the center of ALL the selected objects.
Or is this impossible?

Next, I have to export from Blender an fbx file in which the scale does not change when I import the fbx file into 3D Max.
No matter what I select for output, the objects in 3D Max are way off.

I am exporting from Blender with the scale set to 1.

Any help would be appreciated.
Thanks!

not sure what you mean. here is a few tips to how you can solve it:

Alt G - Move the object to the center
Shift Alt CTRL C - lets you deside where to put the origin of an object
Shift S - Snap the 3D cursor. you can use this to place the origin as suggested above
you can also use shift S to move the objects to the 3D cursor.

you can also go the properties panel (N) and manually set the cursor location. lets say you want it to be EXSACTLY on the X axses, but somewhere on the Y and Z, then set the X to 0.