I haven't used their tags control myself, but I've used the date (calendar), select, form, row, column controls, etc. And actually, in the web app I am working on, I only use struts-layout for the new features, the remaining app still runs old style JSPs. So, just include layout tags in those two JSPs and leave other JSPs untouched.
Also, make sure to put struts-layout.properties under WEB-INF/classes and enter directory information there for both images and config (depending on where you put them). This step is missing from their installation instructions.
There is a Yahoo group for struts-layout:
http://tech.groups.yahoo.com/group/struts-layout/ Also, if you still want to use <head> <body> tags, you have to include <layout:skin/> in the head part.