The problem is, you’ve given yourself 600px of space in between those side images, and you’ve used up all of it. You can do something like this to any of those tables that are now 600px wide. Change the width to 560px and then center it. That will give you 20px of whitespace on the left and right. You will need to do this for several tables that are 600px wide now.
width="560" style="margin: 0 auto;"
(inside the <table> tag)
This is a really bad way of doing it, but it gets the job done. Much better to do this with divs that have unique names, then define the style for those divs in style.css. But, just adding that style inline gets the job done. It’s just not the best way of doing it.
BTW – I just gave it 20px of whitespace on the sides. This forum here has 40px of whitespace on either side of the content. I always thought this forum looked too narrow, so I didn’t add that much whitespace when I made yours 560px wide.