dumb windows question

[Mark B. Elrod]

i cannot remember how to do something under windows. i hope someone out
there does. you know how when you grab a splitter (like in explorer) it
inverts the background with a pattern and follows the mouse until you
release the mouse button? how do you get it to draw that inverted line?
i know this is sooooo simple yet i can't recall how it is done.

help!

elrod