Well, when making a pure SWF, I have never had the problem, as my SWF so far has centered automaticly.
With Weblayout/HTML I have a problem. At first it works fine, but if I put a bézierline and object close too each other then one of them is placed out in left at the "variable space"... If I change which object is in front, then it switches around, so the other object then is moved out to the left (I placed them in the middle, and the objects does not touch the textboxes)... Any ideas?