I'm new to web development, so I didn't have a doctype on my site. I just figured out why I needed it and added a HTML 4.0 strict doctype tag.
In Opera: Now the main content of my page moved to the left, covering up the menu bar. The right, white border of the menu bar is also missing now.
In IE: The menu bar now appears at the bottom of the page instead of on the left as it should be.
My site is at http://thinkdammit.freeunixhost.com/
Thank you for your help!
Quirks mode
When you don't define your document type with the <!DOCTYPE directive the browser rendering the page have to guess what kind of document is. So now you have explicity define, it will render acording to the standars.
Some links of how about Browsers quirk:
Mozilla
Internet Explorer
Adding doctype messes up menu bar
Yay! With help from that page, I got it all sorted out. Thanks!