DW templates are pretty ugly and I haven’t used them in a looooong while.
Assuming they’re still the same as back then, all you do is define areas that are writeable. For the non-dreamweaver, these then look like comments, well they are.
How difficult/easy it is going to be to transfer an existing site based on DW templates, to a new design also based on DW templates depends on the content of these writeable areas, i.e. how ugly/nice the html looks in those.