first of all you should definitely flash your Mac Pro from 4,1 to 5,1 ...
I know you said you were unsuccessful ... but everybody does it (as did i) ...
it is well worth the hassle .
and as David has pointed out the feature you speak of was not available in logic pro 9 ...
if you were able to drag left or right to extend a region ...
that just means that you had already split , cut or cropped that region before
and you are just putting back what you had previously removed .
The best and easiest work around before 10.4 is this ;
just record a one bar region of silence on an audio track somewhere ...
now anytime you need to extend a region with silence
you just copy/ paste that silent region in front of or behind the region you're working on , join or merge them together ...
then trim to your desired length .
been doing that for years ...