If you have fixed width footer just use divs (you can use lists also). No need to worry about htm5, it wil not create columns for you.
Step one:
Divide the footer width by three and get the width of your columns.
Step two:
Add three divs with that same column width and float them left (no borders, margins, or padding here please).
Step four:
Nest another div inside each of the fixed columns. (don't put any width on this one, but you can add padding borders and all your styling here) this way your columns always stay the same width. You will not break the box model.
Exemple (you will use css of course):
<footer style="width:960px">
<div style="width:320px;float:left"><div style="padding:15px; border:1px solid #999">Column One</div></div>
<div style="width:320px;float:left"><div style="padding:15px; border:1px solid #999">Column Two</div></div>
<div style="width:320px;float:left"><div style="padding:15px; border:1px solid #999">Column Three</div></div>
<div style="clear:both"></div>
</footer>