IE6 Firefox layout probs

I have been designing my new site and are having a few problems with the layout.

On low res screens (800 x 600) the layout has a few width problems. I have looked over all the HTML and everything is set to % so it should resize to fit the screen width.

In Firefox the gap between the two columns disappears sometimes. If you view a page with a button and click the button it will resize to show the gap between the two cols???

http://www.option-trading.com.au/free_stock_and_option-downloads/free_option_pricing_calculator.asp

When viewing the forum at 800 x 600 it is totally messed up and displays half off the page.

http://www.option-trading.com.au/forum/

Any ideas how to fix the above issues?

Thanks

yeah that's what i develop in and it's all good but when i check it on 800 x 600 it craps out.

I am playing with CSS styles now to get rid of some of the tables.

Do you know the difference between using:

<div ID="content"></div> with a CSS style of
#content{
    float:right;
    width: 78%;
    margin: 0;
    padding: 0 0 0 0;
    border: 1px solid #000000;
}


or using

<div class="content"></div> with a CSS style of
.content{
    float:right;
    width: 78%;
    margin: 0;
    padding: 0 0 0 0;
    border: 1px solid #000000;
}

does it make any difference of is one better then the other?