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I am not sure what exactly you are asking.
However, Templates vs. Themes here.
Templates are used to control module output. Any table withing a template can be modified to be more flexible.
In most cases when you find that a template (i.e. viewforums.html) causes your theme tables to break, it is because the tables are fixed width. instead of using a px based width try a % based.
Now if you are speaking of Theme tables. The Same pretty much goes for this. Unless you REALLY need to use a px based width I would always recommend a % based. The only time you should really have to use a px based width is if your theme is graphically intensive.
You also have to take into account that different users use different resolutions/browsers. Try to create flexible designs, and modify things to work across the globe.
Again though, if you could provide an example of what "table" is being broken by what. Perhaps we could be of more assistance.
BOL.