XSI? not me, tho i never asked... only thing i can help is with opacit, and even then, it aint much. Best idea for that is a Wacom Tablet, a cheap graphire does a fine fine job. as for control z, it can only go back 1 step, and pressing it again i believe goes forward again. as for the layers... possibly, tho i never thought of it. Check the index of the help guide, and run a search. Usually with commands that have shortcuts, the shortcuts are listed.