Wonderful Web "Standards"

I've just noticed that my LLC's site looks like crap in IE. The left sidebar doesn't display, only the colored background, plus the margins are all crappy. Arrgghh. I thought I'd checked all this out in both IE (sucky) and Firefox (killer). My CSS and XHTML all validates, so now it's off to delve into the subtle "feature" CSS handling of IE. Hopefully this was something in one of the last couple changes I did, otherwise I'll have had a long period of lookign like the web design bozo I really am. Ptooey.