You can simplify it to:
@confirm:Really sort to alphabetical folders?
Rename FROM=* TO="{=f=Left(Trim(file), 1); IsDigit(f) ? "0" : f=}\*" IGNOREEXT AUTONUMBER
No need to select anything, you can tell the Rename command to work on all items. (Although I am not sure that's really a good idea here, as it would move any letter folders that already exist into themselves.)
Please check out Formatting tips specific to the Opus forum for how to post code blocks without characters like \ and * causing problems (and so I don't have to keep editing your posts :))