This is odd. IE finds these message boards no problem, typed just like this in the address bar:

Catholicrecordsociety.org/business
Stgabrielradio.com/forum

... but for this other one, I don't get a typical "page not found" page, but a pop-up (see below):
Geneocity.com/boards

... why does IE not find the one at geneocity.com?
If I put - Index in the address bar it finds it no problem.

What's up with that?

Are you using IE7? Perhaps it's a matter of setting the search provider correctly:

http://tredosoft.com/files/pictures/provider.gif

Click on Change Search Defaults and set it to Google.

I'm using (well, not using - but have it for testing webpages) IE6.

And most odd is that regardless of my settings, it's finding the first two using only domain.com/folder but not the other one.

Actually it's a matter of the DNS entry. Some entries require the WWW others won't.