WELCOME TO THE ORG!
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Now..

I havent tried the RTW editor..
But i beleve its for Editing terrain.

IN Shogun Total War. you could not use the editor Unless Your GFX options were set to hardware mode.
It refused to let you click on the Edit button if you were using Software mode,

Prehaps this is true for rome as well.

At the moment RTW is uninstalled "again" So i cannot go and check if this is true.
If i am not correct dont worry As I am prety sure Many more will answer your question(s) for you.