Googling your situation
http://www.google.com/search?hl=en&client=firefox-a&rls=org.mozilla:en-US:official&q=ie+7+table+disappear&start=10&sa=N
it looks like IE7 has a css conflict or bug.
Another thing to know is that IE builds tables from left to right while FireFox and most other browsers build them from right to left. (I may have this reversed since it is very old news.) Thus, you know where to start looking for troublesome code.
Text editors
Tables Not Viewed in Internet Explorer 7
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