In my experience percentage is best for defining the table. IF you are using a border background and want to keep text out of the border, the next step is to define your first
*in pixels* - and force it to be that wide by putting in an invisible gif exactly that wide. Be aware that any images wider than about 630 pixels (minus the width of your border column, if any) will roll off the right side of the screen for anyone with a screen resolution of 640x480.
I am going to be writing a tutorial and posting invisible gifs at my Free Graphics website (http://members.tripod.com/~Echo0) soon, but it isn't there yet.