If you don't want postbacks you shouldn't use DNN or any other server side CMS.
Server side scripting relies on postbacks. You could try a CMS that generates regular HTML, but the best way is to convince the client that his demand is prehistoric.

If you don't want javascript asp.net can switch to a javacsriptless mode (that's what happens if .NET (1.1) cannot determine the brouwser.
You could force a site to render as non javascript compatible by editing you machine.config but I think a lot of the functionality of DNN relies on Javascript.
(but I think this also limits the CSS possibilities)

People don't like javascript because of security most likely will use Firefox instead of internet explorer, since most websites will not work without Javascript.

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