Hi Barry,
We also use the alter banner like Randy. In addition to modifying the banner.txt you'll need to add the following line to the codebase/netmarkets/jsp/util/begin_custom.jspf:
<%@ include file="/netmarkets/jsp/util/banner_custom.jspf"%>
Restart Windchill and you'll have the banner. It will update in real time, with no need for a restart. If you want to take it down, clear the contents of banner.txt and leave it blank. It will disappear. We leave ours blank until we have messages to send to our users.
For more information check out the customizers guide.
-Adam