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!
Adding doctype messes up menu bar
Yay! With help from that page, I got it all sorted out. Thanks!