The easiest thing to do is to override room descriptions throughout the game by specifying your own description script.
There is a sample at
http://www.axeuk.com/quest/developer/do ... ptions.htm which will generate a description similar to the Quest default. Open your ASL file in Notepad and paste the script block into the "define game" section. Then open your game in QDK and you can edit this script by selecting Game from the tree menu and going to the Advanced tab and editing the "To describe rooms in the game" script - you can add the clear screen command at the beginning.