At first controlling a 7 segment display seems quite complex but it quickly becomes clear.
What follows is a quick guide to control a 7 segment display with a arduino board
If you want to jump ahead to any other part here's your chance:
Step 1 - What Is A Seven Segment Display?
Step 2 - Parts & Tools
Step 3 - Testing
Step 4 - Built The Circuit
Step 5 - Project 1- One Digit Count Down Timer
Step 6 - Multiplexing
Step 7 - Project 2 - Two Digit Count Down Timer
This instructable is a entry in the arduino contest so if you like it please vote.