I'm quite new to struts too but I think you're misunderstanding the purpose of the struts-config.xml and tiles-defs.xml files. Is that excerpt from your tiles-definitions file? All that stuff should be in your struts-config file. An excerpt from my struts-config.xml:
Then 'product.detail' is defined in tiles-deinfitions.xml as being an extension of the main layout, except with differing title and content value:
I've built my struts application up this way, by using my struts-config file to forward to various tiles depending on what has been selected, then defining these tiles as being extensions of one overall layout but with different jsp pages populating their content area. Hope this helps - it sounds like you need to read a bit more about struts tiles: courses.coreservlets.com/Course-Materials/pdf/struts/10-Struts-Tiles.pdf
Now, can anybody help me with my problem? (see first post in thread)