What Do I Need to Know When building a PC for CrossFire?

get a motherboard with all the slots you need that won't be blocked?

Every m/b I've looked at most, if not all, the other slots are blocked when two of these cards are installed.

MSI X58A-GD65 LGA 1366 Intel X58 SATA 6Gb/s USB 3.0 ATX

MSI X58 Pro-E LGA 1366 Intel X58 ATX Intel Motherboard

GIGABYTE GA-X58A-UD3R LGA 1366 Intel X58 SATA 6Gb/s USB 3.0 ATX Intel Motherboard

I read someplace when using crossfire the cards should not be adjacent to each other.

what slots do you need?

I don't know. Do gamer PCs use add in cards? This will be my first gaming PC. Will use i7 9xx CPU.

If you're talking about PCI slots, then there really isnt much to put in them anymore.. Modern motherboards come with just about everything you would want to add with a PCI card.. ie: Sound card, more USB/Firewire, ethernet card. I think you will be hardpressed to find a motherboard that DOESN'T come with this options at the same time as supporting two or more PCIe cards.

I would be more concerned about the case you buy.. Make sure it's large enough to accomodate two long cards without pushing into/hitting the drive bays.

Also, make sure either the MOBO you buy or the video cards your buy come with a crossfire cable.

it depends, i use a wifi card and sound card on mine. some people just use the mobo's built in sound, modem, and/or wi-fi.

it seems like you will be fine though since you don't need those cards from your question.

Good points. As stated these are very long cards (10 1/2" long) I really want to stay w/ a midtower case if possible. Since I sit so close to the PC I want it to be as quiet as possible.

Any case recommendations?

I think this one might work:
http://www.tigerdirect.com/applications/SearchTools/ite...

like a card reader on the front bezel.

yeah that's a very good case. newegg has the blue fan version of it

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I like it as it is 22" deep. Too bad I had to sort through a lot of cases to find it.
the case i have now is only 18" deep but the left side of the case has air vents on it which leads to a large venturi shaped large plastic funnel that leads directly to the CPU fan which seems to be pretty efficient cooling.

anybody know of other 22" deep cases?

When picking a motherboard, pick one that will allow you to have an extra space between the SLI/CF GPU so that they can breath.

Found several ASUS and Gigabyte boards that'll work.

Background:
I started with the intent to eventually move to Crossfire/Eyefinity, so I started with a single monitor/vid card but took care that the components could handle the additional load later.

For Case:
Look for at least 22", you would be surprised how many mid towers can be so long. I have a COOLER MASTER HAF 922 and It easily fits a 5850, I am pretty sure it will fit a 5870.

For PSU: I got OCZ StealthXStream OCZ700SXS 700W which can handle the 1 DvD drive, 2 5850s and 1 500GB drive. I wouldn't recommend using this PSU with dual 5870s or nvidia cards.

For MB: ASUS M4A79XTD EVO AM3 AMD 790X ATX AMD Motherboard. I just instaslled the second video card and it's snug but decent, and I believe the bottom PCI-E slot is actually available. But it has all the inputs you'd ever need so I wouldn't worry about that. The 8x8x PCI for XFire hasn't proved to be a problem.

For Monitors: I have 2 DELL 1280x1024 monitors flanking a view sonic 1280x1024 (origional screen). I personally thing that the 5:4s give better viewports in games, however developers haven't mastered the screen geometry yet so 16:9 movies look stupid as they bleed into the side monitors instead of the video being cropped to fit in the center 5:4 box. But that's something I live with since the 2 Dell monitors was only 150 bucks total.

That's very helpful. Is you PC very noisy? My computer chair is next to the PC so if it's noisy I'm going to know it.