Are the tables in pixels or percentages? And is some of the text in tables without visible borders?
If the website has used pixels in the creation of these tables then I think the solution is perhaps relatively simple. Go into the table properties and change to percentages (whilst in theory you should be able to have 100% you might want to make it slightly less - it is all about experimentation).
If the table properties are already in percentages then maybe some of the html coding has become corrupted. I happened to notice that your home page was rather long and wondered whether it would be easier to split it into several topic specific sub-pages (this is what I did
for the Euphonix Choir website (euphonix.org.uk) - the homepage has several sub pages. If you have subpages then identifying the problem may be easier to spot - sorry just an idea.
Let me know how you get on.