One tier sitemap help SEO ?

I’m building a site, the navigation is text links, the navigation is only one level.

Client says that he expects a sitemap as included in the package, as it helps Google find the information on the site.

I’ll add one, but I’d also like to mention to him that the reason I didn’t add one in the first place was because it wasn’t necessary, and won’t help Google wise due to the navigation already being on the page.

How right would I be?

TIA

It sounds to me as if you’d be 100% right. If the sitemap is just a repetition of the navigation links, then you don’t really need to repeat it (though whatever the client says is always right, no matter how insanely stupid it is). Just make sure you use link titles and other SEO-friendly code in general.

Of course your client may be talking about a Google Sitemap, which is a different (although functionally equivalent) thing:
http://www.google.com/support/webmasters/bin/answer.py?answer=34654

And of course this being MODx someone has created a contribution to create those:
http://modxcms.com/GoogleSiteMap_XML-592.html

Agree.

If the site is 10 pages and all 10 pages have links to the other 9 pages, then nothing will really be gained.

But if the site is 100 pages, but only 10 main links in the navigation for the main 10 pages, with in page links throughout for the other pages, then it might help.... whether they are all at the same level or not doesn’t really matter-- I don’t think that is the case, but just wanted to clarify.

As for the xml sitemap, this is a different case entirely and there may be some benefit, although, if the site is like the first case, even that will probably be minimal.