brainbuster no. 31 - do or die

This competition closes on Sunday 31 October 2010.

Check the rules before entering.

the brainbuster

An apparently straightforward one this time:

In how many different ways can the numbers 1 to 6 on a die (cube) be marked? As usual, the numbers on opposite faces must add to 7.

Give your reasoning.

thinkingpeoplefirst