If the page is on a test site can you post the URL to it here for us to look at ?
That will allow us to see the source code and find out where things are breaking.
Without seeing the underlying code, I'll take the following guess:
Chances are that your page contains contradictory code.
If your table is set to 600 pixels wide and it has objects in it that are larger than this pre-set width then things wil start going all over.
In general you should set each table cell up to be whatever width of the parent table is desirable.
A 750 pixel wide table may have a left hand column for navigation buttons and links. This left hand column would be best set at, say, 200 pixels wide. Obviously this would mean that the main content cell should be 550 pixels.
Now, to break this nice layout, let's say put a 400 pixel wide image in the left hand column. Obviously the image is wider than you specified the column to be, so you'll throw everything out. Since the main content column in this example is set to 550 pixels wide, suddenly your page has a 400 pixel wide image in acell that is too narrow for it plus a 550 pixel wide fixed width table cell. All that adds up to horizontal scrolling and it throws everything else in your page out in relation to it.
Upload the page to a test folder on a site if you can and we'll look at it, but my first guess is that the page elements contradict their pre-set dimensions.