I gues you could use conditional statements around the tiles tags.
I based this example off of
http://struts.apache.org/1.x/struts-tiles/examples.html though i would use the jstl <c:if> or <c:choose> tags instead of the scriplet conditionals.
and usually I create a tiles-defs.xml and put definitions there and have it installed with
struts with the tiles request processor. (see link above to the tiles documentation site) and if i do any dynamic switching in the jsp, it would then be with the <tiles :p ut> tags within a conditional construct.
[ July 03, 2006: Message edited by: Travis Hein ]