CSS cross browser problems

I know there are a lot of articles lying around about this problem, but im having trouble with css layout for a site im working on,

in IE6.0 the site displays as it should do.

in Opera 7.23 + 7.11 the site displays with the main text sitting on the logo for the page,

in firefox it displays as it does in opera.

I am using includes for the full page with no html in the index.php page, i have tried this without includes bur get the same problems as before.

the site addy is:

http://www.kptspanishproperties.org.uk

any help wpuld be great, also im not using tables just using css for all the layout needed

first of all try to validate your site, with w3.orgs validator,
you have some faults in your markup. lacking ending body/html tag, and you haven't closed some of the images.

you should also drop attributs, like width, border, align from the tags, and use css to achieve the wanted effects.
also drop the center-tag it has been deprecated in this dtd.

don't use br-tags to create space use margins in css.

don't use bmp picture files, use either gif/png or jpeg,
that logo is almost 400kb


remember both opera and mozilla follows w3.orgs standards more correctly than msie. so they display the page as it should not msie,

msie wrongly accepts width asigned to inline elements,

like <span class="topnav" width=100%>
use div instead, (and drop the width as mentioned)
<div class="topnav">

instead of center use text-align:center;

i aslo see that you have used verdana with font-size 10px,
read this and see why you should avoid this
http://www.virtuelvis.com/archives/146.html
http://www.xs4all.nl/~sbpoley/webmatters/verdana.html