onChange is an event handler, if that event doesn't occur it isn't 
triggered. maybe onBlur is what you need.
if you  explain what you are trying to achieve, there is probably a way to 
do it, or check here:

http://netscape.zdnet.com/framer/hud0022460/www.zdnet.com/devhead/filters/0
,9429,2133214,00.html

joe