When you validate your CSS file, do you get a load of warnings about
background-color not being accompanied by a
color and vice versa?
More on I’m getting CSS validator warnings →
Usually when people have trouble with floating columns it's because they've specified a width where there doesn't always need to be one.
Variations on this question can include:
- Can CSS insert content onto a page?
- How do I update the content of multiple pages from a single file?
- How can I get CSS to behave like frames?
One of the easiest methods of giving your site the appearance of the columns being the same height is to used the Faux Columns technique as first outlined by Dan Cederholm on A List Apart.
More on Why won’t faux columns work? →
If your site looks right in a browser like Firefox, Opera or Mozilla, but not in Internet Explorer, it's highly likely you're being affected by one of IE's numerous bugs.
Fortunately, most of these have been well-documented at Position is Everything.