You don't really want conditional HTML, you want conditional CSS. There are other tricks to make CSS only work for MSIE, for example, see this for an example. According to that page, you can specify CSS style properties with a leading "_" prefix, and only MSIE will pick it up (coloured blue in the syntax highlighted HTML example). I haven't tried it, but it is worth a shot.

Googling for CSS underscore hack, and following some links, I ended up on this page: The Underscore Hack.