Yeah, I hear your pain. It actually depends on the browser to obey the directives you put in the HTML.
I got sick of trying to make these things work in all browsers, but I kind of found a way that works in (so far) 5 browsers. What I do is make the table 100%, but make it two columns wide. The first column would have the stuff that you want only 80% of the page, an the next column has whatever you want on the right (maybe even just a spacer).
<!-- Whole Page Table -->
<TABLE WIDTH="100%" BORDER="0">
<TR>
<!-- Your main stuff in this cell -->
<TD WIDTH="100%">
Your Main Stuff In Here
</TD>
<TD WIDTH="144">
Spacer or other stuff here
</TD>
</TR>
</TABLE>
This seems to work in most browsers, but sometimes for IE I need to put an invisible png or gif file in the second column to make it hold its width.
HTH
-- Rich