<snip More detail on step one is needed. Using the Insert Table command (ALT+N,T,I), what is in the combo box next to the radio button you've chosen for fixed width?
<snip My guess is that you want a tidy table where the column width for a given column is that of the widest item in that column (provided you're not dealing with text that is very long), and the easiest way to get that is to choose Autofit to contents rather than fixed width.
You have given me a solution to the problem of creating tables which is crucial. However, I wish NVDA would alert me to badly formatted tables.