Setting up crossfire for the first time.

[Cooners]

I have just got hold of a cheap 4870 which I am going to crossfire with my existing 4870, but this is the first time i've ever set up crossfire so just want to check a few things.
1. How many crossfire ribbons should i use, i've noticed some with one on and others using two.
2. Is there anything i need to do to turn crossfire on or will it just detect the extra card and turn its self on?
3. It there any extra drivers i need to install?
4. Is there any pitfalls I should watch out for?
Thanks

 

[Cooners]

Thanks for the advice, will get this done at the weekend.