dirtyjumbo - I've found the safest thing to do when using tables inside of tables is to make the outside one a hard width (like 600 pixels) and then to make the inside tables & cells a % value.
So on this one, if the outside table is 500 pixels, take the inside table & make it 100% & then the cells 33%.
By doing this, you'll almost eliminate the problem of having tables extend outside of other tables in pretty much every browser
