this may or may not be of help.. you cannot fix a table width any more than you can fix it's height, a table by it's very nature will stretch. It's what it does it's why everyone likes them, until they can't fix them! (fix as in restrict)
so thank you alt for clarifying the other widths/heights but they do not matter
my guess is that the screen that is not forcing the scrollbar is the one that actually really does fit into a 1250 layout
my advice is (and I've never been a table nay-sayer) is do not try to make it do magic, even tables can't fix everything, they haven't been able to do that for a very long time!
It's boring maths most of the time, and I don't want CSS to be able to do maths.. if I could see an example of this I would be willing to bet that a block formatting context might help (not necessarily Laura's son, but logically!)