404 error on all page and post links

Just installed 2.6.5 via Andrea's new Installation Guide for Beginners. Everything seemed to go fine but when I try to visit pages or posts on the main blog or any sub-blogs I get a 404 page. Wildcard sub-domains have been enabled by my host (not that that matters here necessarily) Everything looks fine on the surface but I'm getting these errors on page/post links.

I have another WPMU test site that someone else setup for me, on the same host, and it works fine...so the problem is probably me and my setup. Can someone help?

The error log indicates the files does not exist but of course the pages and posts are there.

Any assistance would be appreciated.

Thanks