Sure that shouldn't be to big a problem and I can think of a couple of ways you could do it at least for the static pages.  If you are using a web.config file you will have to merge it with the DNN web.config file and things should work fine.

I would put all the old site in a new folder just to keep track of it then in DNN you create your site recreating any pages you want from scratch and pick add a page for your old stuff you can then either select the page to link to an existing old file or for the static pages add an HTML/Text module and copy all of the html from the old page to the module.  If you do that it will be editable by whoever you give permissions to edit for that module.

Pretty simple but a little time consuming.

Cheers,