Ok, first of all your html is wrong...
You're using <br /> to space out your paragraphs when you should be using <p>.
A fix for what you want to do, in a hahahahahaha-rigged manner, would be adding a height of 700px (height: 700px;) within #main.
But if you want it to work with any amount of text, i would suggest replacing those BR's with P's first and experimenting more. I'm no css/xhtml expert myself but I've done enough of my own projects to know that it is possible and it just requires a lot of fucking around with... and also, I know enough not to ask on GFY LOL.
Go to sitepoint.com and post in their CSS forum, or webmasterworld. You'll get better responses.