Well,for one you’re using tables. Bad. :)
But otherwise it looks like you’ve probablly left a table row/col open somewhere so the content is flowing over the whole page.
I’d say get ride of the tables, start fresh with CSS and HTML :D
If you don’t want to get rid of the tables, then got to the w3c.org and validate your code. You’ll get a list of errors and warnings, which after you fix should fix whatever problems you are having!