Upon a fresh install of KDE on Debian Squeeze I found that all of my readings where in metric units and 24 hour unites. Which is fine, however I am a lazy American who likes things in the obscure and outdated imperial units and despite my time in the military, I prefer my clock in 12 hour time.

In the System Settings go to Regional & Language under the Locale I add US English. Under Time & Date I change Time format: to pH:MM:SS AMPM. Then I hope over to the Other tab and set Measure system: to Imperial.

Restart KDE.