When I first refreshed my Geocaching website, using the 960 Grid system, I found that it didn’t render properly in IE. To be honest it wasn’t a problem for me as an OS X Safari user and I did check it worked in Firefox, Opera, Chrome and even Epiphany (just in case there are any Debian users visiting my site).
Anyway, it had been bugging me a bit so I’ve cleaned up the code and reverted to HTML 4. That seems to have done the trick.
I found a couple of pretty helpful on-line tools, so here are the links here in case you find them useful too.
W3C Markup Validation Service: http://validator.w3.org
IE NetRenderer browser compatibility check: http://netrenderer.com