rendering issues

As a newbie, I was wondering how all of you discover how to fix your rendering
problems in various browsers. For instance, I have a site that is not
rendering a 'border bottom' correctly and I have no idea how to fix it or where
to look for info. I want the border to appear BELOW the address in the
header, but in Opera and Safari only, the address is showing up at the very top
of the page. I will list my URL below, but be forewarned...the side margins
are not working either so it looks terrible at the moment (I have a separate
post regarding that also): http://kidtalksls.com Thanks, Tracey