Minimal Site

[Wishbone]

If you set up config.php and .htaccess, you can make all your URLs end up with .htm

[uniqu3]

You can not keep your current site "the way it is" you would have to create a Template in CMSMS based on your current site and move your Content, but as Wishbone mentioned you can create URL exactly the same as on your current site see Pretty URLs Documentation

[velden]

If you ONLY use {content} it would be quite simple:

Make a very basic template, consider using only the {content} tag in it.

Append ?showtemplate=false (or &showtemplate=false if it's not the first url parameter) to the url your calling with $.get and you only get the content of {content} --> maybe that's not even necessary if your template only contains {content}

Make sure however that CMS does not override the default index.htm with its index.php. Check that first. Else you could install cmsms into a subdir.

That said: I don't know why you would make it this way. Invest a little more time and you have a full cms website. It can even be fun to do! And you're sure the content is served to clients. What if a client does not allow for JS? (I know, I know)

[staartmees]

You're looking for unneccesary problems by trying to use cmsms in a way it is not mentioned to be. Just use cmsms in the way it's mentioned to.