Page askew under 800 x 600

[Lin]

Hello. I have a problem with my web page, which is in three columns - table at 95%.
My third column contains a few images, and although the page looks okay at my resolution of 1440 x 900, when I view it at 800 x 600 the third column has expanded and the page is askew. The pixel width of the column is 320 and none of my images are over 200 so I don't know what is forcing the third column wider under a lower resolution . .?

Thanks,
Lin