I may be wrong, but from the looks of it, you must be starting to work with html/css. If the site you have shown here has been done with tables (which is not recommended semantically), I suggest that you use absolute measurements in pixels in the width and height of cells, rather than relative measurements (percentage, on, and so on). Try using fixed width for the main table or container and accommodate the elements with bounded widths.
It would be interesting if you use some kind of CSS Reset.
The recommendations posted by friends here are very valid, however, the learning curve and mastery of most of them is quite long. I advise you to study more tableless development using HTML and CSS and only then start using frameworks. With that alone you’ll have a long work ahead of you.
I am giving a closing vote because the question is too vague to say what is the cause of the problem. If you want to elaborate more (although I have already accepted a response), I believe that the content can be more useful for future visitors to the site.
– bfavaretto