Ohhh, First of all you have to download the latest MP to ST4, but...
Prior to ST5 you couldn't create an "position associative assembly mirroring", what you want now.
This was new in ST5!
If want this you'll have to migrate to 5 at least
Associative mirror functionality is available in ST5 and later versions. The old behavior (non associative mirror) is still available through the application program interface and delivered in the custom folder in the product directory