Pranks for April Fool's Day 2004?

Nighttime asks: "April the First will soon be upon us and I'm looking for some subtle pranks to play around the office. There's the usual taking a screenshot and setting as background, placing a piece of tape across the mouse ball (use opaque tape for optical mice), setting the keyboard layout to Dvorak, swapping the 'M' and 'N' keys etc. The office empties quite quickly at the end of the day which leaves plenty of time for preparation."