Table and column widths

I need to create a table which initially has two columns in it. Both will
contain text and sometimes have a bottom border. When there is a bottom
border I want the border to start and finish where the text starts and
finishes. To achieve this, I have made the left and right cell margins 0cm.
This seems to solve that problem initially - is this the correct approach?

The next problem I have is that I need the text / bottom border of the first
column to start exactly 3cm from the left hand edge of the page and the text
/ bottom border of the second column to start at exactly 3.6cm from the left
hand edge of the page and end 3cm from the right hand edge of the page.

What is the best way to achieve this?

I shall later be adding rows and splitting them into more columns. I always
need the table to be the same width – I want to be able to specify EXACT
column widths rather than just preferred. I don’t want Word to override my
table / column widths.

I am a sophisticated user of Word but do not do programming.

This is getting to be a bit of a nightmare!

I am using Word 2003 but need to save it in the format Word 97- 2003.