The following are tables with two cells. The first cell contains two buttons and a separator between them. The second cell has a &nbsp; and its width is set to "100%", so it forces the first one to shrink as much as it can.

&nbsp; as separator (using nowrap) (bug on Opera):

Space as separator (using nowrap):

&nbsp; as separator (without nowrap) (bug on Firefox):

Space as separator (without nowrap):