Anything i need to know before installing a SLI system?

I am making a pc for a friend and I was wondering if I should take anything into consideration before going ahead. I am buying him 2X6600GT's by Gigabyte, they are identical and are PCI-E. I am assuming they come with cables.

Do they need to be in PCI-E slots next to each other?

What cables link them together?

(By the way im installing it on a 939 Amd64 system)

Alex

Hopefully this is obvious, but as it wasn't clear in your post I'll say it just in case.

The motherboard has to be SLI ready. It will have two special PCIe slots made specifically for SLI, and the cables that will be needed come with the motherboard. What motherboard are you looking at?

I was looking at a Gigabyte motherboard bundle:

http://www.ebuyer.com/customer/prod...2hvd19wcm9kdWN0X292ZXJ2aWV3&product_uid=85287

I know its a very good brand, and it comes with the graphics cards ready, I was just wondering what else i should consider when installing them.

Alex