why does the effective min width appear to be like 1250 instead of about 960px?

I have a simple brochure type site with a couple pages:
http://edwardsvilleregionbreastfeeding.org/
And making the browser window smaller than about 1250 causes a scroll bar at the bottom.
try making the browser window about 960px, and the person reading the page has to scroll right and left to see the About Us text. The stuff on the site is so simple, I would think I could make the window really really narrow, and it would still be able to display.

What I notice, is that when I "reload" the page, for an instant, the scroll bar disappears but then it pops back up again, like as if itwas loading stuff to fit ok, then loaded one more thing and made the min width bigger.

I also noticed a similar thing on the "try a demo" site that is linked from the project page, a bunch of blank space on the right side.

What do I have to change in the css, to let the min size stay around 960?