http://www.envirosmith.com/about_Us.html

Check out this page in both IE and FF can you tell me why the bottom is not showing up on FF but it is on IE.

Anyone good enough to take a guess before looking at it?

I guess it is... because of some error in your code!

And lookie, I was right.
http://jigsaw.w3.org/css-validator/validat...;usermedium=all

What do I win?

You need to fix your HTML-XHTML mix too. Decide which of them you want to use. You can't have both.
http://www.htmlhelp.com/cgi-bin/validate.c...s&input=yes

I have an old piece of cheese in the fridge, but that is about it. Will that do?

If I can't use < br > then what do I use in its place

Cheese is fine. Love cheese, me.

Judging from your question, I'd say you should rather use HTML 4.01 than XHTML. If you are dead set on XHTML, please read about the differences with HTML here.
http://www.w3.org/TR/xhtml1/#diffs

I will want more cheese for this but I can tell you it's the parse errors the CSS validator reports that make part of your CSS not show up.

<br />