Table spanning

hey, I know that most of us have better resolutions then 800x600 but I still want to design for that resolution. Well I have a table with like columns. I want the 5th column to expand the whole width of the extra screen. So depending on which resolution u had it still went all the way. i know you can do this with percents. Hoever how would I just do one cell, or do I have to do the whole table?