I was creating a new site which has three backgrounds creating a border around the page with cut outs etc, and I kept finding that in NS and Opera I would always get a thin line where the table borders should be (even though border="0" etc). Now I use an external css and found that if I have a space between

p {color: #000000} (using P as an example changed for all)

then NS and Opera give you this line but change it too

p {color:#000000} NOTE space gone between : and #

the lines disappear....!

Now not really sure whether this is true or not BUT thought that I would share this incase anyone else finds they are having the same problem.