Div not wrapping with float left

Hi. I'm trying to create a page with a menu on the lefthand side and a main text area besides it, but firefox renders it with the text area way down below my menu. I cannot figure what I'm doing wrong.
The page validates as xhtml 1.0 strict.

The menu bar has float:left and clear:none. the main text area has float:left clear:none. It works in IE, why?

Please help me or I may be forced to go back to using tables.
Carol.

Well, i figured a way around it, and that was not to float the main text area, putting some padding on the menu div.

I have a new problem now. (I'm obviously a css beginner ) I want a border down the left and righthand side of my main container div. I've set it to 100% height so that it fills the browser window, but when the page is longer than the browser window, the line stops at only being the height of the window. My menu container div, though, extends down to the bottom of the content with a border longer than the main container. Any ideas why please?

Carol.