Cross-Browser Compability

Cross-Browser Compability

Hello,

I'm doing the xHTML\CSS coding for a customer that's also a friend of mine. I don't have a vast experience on the web-development area, but I'm graduating on computer engineering and I do my work with pleasure, so I'm always trying to acquire more knowledge.

Anyway, one of the main difficulties that I'm having working on web-development (rather than developing common desktop applications) has to do with the challenge of creating xHTML\CSS code that's cross browser compatible.

I've read the W3C recommendations and tried to stick to what they recommend. All the xHTML\CSS coding I've done passes the W3C validation.

Everything works great on recent browsers (Safari, IE8, Firefox, Chrome), but when I get to Opera I just can't get it right.

I was wondering if there's someone who could help me:

1. What am I doing wrong? Why does Opera interpret the same code that works on all the other browsers differently?

2. I'm developing a second CSS file for IE7 (who also is giving my headaches). Is there a conditional tag like the <!--[if IE> tag for Opera?

You may check the problem here:

http://diogoosorio.webuda.com/

Please don't mind the header and the menu. I'm still working on them.

Thanks for your help!