Define fixed. Must the footer ALWAYS be stuck at the bottom of the viewport, even if there’s enough content to push it aside normally, or do you want the footer to appear at the bottom of the viewport ONLY if there isn’t enough content to push it over, but to act normally if there is?
The former requires the use of position: fixed; (not supported natively in IE /5/6) whereas the latter requires some extra (and ingenious) markup. Both solutions can be found in the CSS FAQ at the top of the CSS board here on SitePoint (I’d link to it, but I have to head out to have a tooth extracted).
The footer has to sit beneath all other content. Whereas, I want the footer (which sits at the bottom of the first of three columns) to always appear at the bottom of the viewport, even if one of the other two columns stretches past the bottom of the viewport.
I tried the alternative which was positioning it at the bottom of the first column, but this does not seem to re-size depending on the size of the viewport.