CSS Positioning, cross browser problem

Okay this is probably a dumb newbie style question but why does this work in Mozilla but not in Opera or IE?

http://www.diypromoters.co.uk/sitedev/index3.html

..or should I be doing this in a completely different fashion?

if you use this style:
iframe.main_window{position: absolute; top: 162px; left: 206px}
it will work in IE and opera7.

Don't know about mozilla....
But you may need a diff style for mozilla...

Browser sniffers will always be needed..it seems.

According to the CSS spec you are not allowed to use underscores in class names so you should probably take that out. Hyphens are acceptable though.

Really! Oh there's my php spilling over into my CSS

I've actually solved the issue.

I had the positioning defined in the css for the table that has a background image. If I revmove this postioning and define it for a <div> and nest the table in the <div> tags its positioning is the same across the browsers.