2. Your small banners advocate "clavius.org", but this address doesn't work - only "http://www.clavius.org". I think you need to set up a redirect of some sort to make the URL work without the w's.
The banners, when clicked, go to www.clavius.org. Manually typing the URL when you can just click the banner seems like a lot of unnecessary work, but I guess some people like to do things the hard way.
I do find it strange though that clavius.org works in Firefox but not IE. The same problem occurs when you type nasa.gov instead of www.nasa.gov so it might be an IE glitch. But I also tried thespacerace.org thinking that it might have something to do with the .org domain and the site loaded properly, so it must also have something to do with the web host.
No mystery to the different browser behavior: some browsers are programmed to try different addresses under the hood if the first one is a DNS miss or a rejected connection. So if clavius.org port 80 (the normal HTTP port) doesn't resolve or answer, the browser will try www.clavius.org to see if the address resolves differently. I'd really have to slap a traffic analyzer on it to see for sure. And I don't wanna because there's really nothing I can do about it. I'm sure I'm being hosted virtually, so there may also be an HTTP redirection at work with possibly wonky behavior.