Basically if you have a number of pages that are associated with say, template1, and you want to change template1 then this is easy, and you simply change the template and update the pages. If you want to change SOME of the pages to use template2, then you would have to detach the template from these pages, remove the markup you don't want, and attach the new template.
DW is pretty unforgiving with it's templates, so if you have the ability, I'd suggest using server side includes (SSI) instead.
----------------------------------------
Sometimes, when my code just won't behave, I take it outside and make it listen to britney spears music, and when it comes back it's really well behaved. I wonder if it's suffering from post tramatic stress syndrome now..