ok ill help you out, I am actually building a system right now, and its 1400, and will cooook butt 5 wows.
What you need when you are setting up a computer.

First of all you need a CPU (processor), this is what runs ur computer, there are choices hear based on how u want ur comptuer to run, the Q9000 or w/e will prolly give u good proformance but if u want 0 lag in dalaran and in wintergrasp or in big raids, go with the i7 920. This will give u all the power ull need for 5 wows. http://www.tigerdirect.com/applicati...sku=CP1-I7-920

Then you need a motherboard that will support your CPU (the i7 920), it will tell u in the specifications if it supports the i7's.) Then you need to look in the motherboard how many memory slots it has. Depending on the amount of memory/type you want each one will support difffernt ones. For wow to cook 5 wows i would reconment 8gigs or ram, but I like the motherboard i got because it supports 12, which gives me ram to have itunes, vent, skype, and internet open and all that also. http://www.tigerdirect.com/applicati...&sku=A455-2868

Memory goes with ur motherboard. I would reconment Corsair because it has a lot of great reviews, go with DDR3 memory, and get 8-12 depending on ur motherboard. the motherboard above supports 12 memory of 1000Mhz, to 2k mhz. So for memory I go with http://www.tigerdirect.com/applicati...8&sku=C13-7100

The you need a video card, for the most FPS, go with the nvidia gtx 275, this will give you extreme FPS in all windows, like 60 or 80 in main, and like 30 in others hopefully, depending on settings. It is cheaper than the 280/85, but it gives you the power, go with the 85 if u want more proformance... http://www.tigerdirect.com/applicati...&sku=E145-0276

Then next, you need a power supply, 750watts is good but more is better, giving ur computer more juice to run on. A corsair 750 is like 140, but for some reason on tiger direct.com, there is a 1,000watt for only 99$... So go with that one http://www.tigerdirect.com/applicati...&sku=A406-1116

Then cooling, this is important to keep all this awsome rig cool so it doesnt crash while going to work on the wows. I would go with a big CPU/case cooler for ur main cooling like a cool master v8, or this one http://www.tigerdirect.com/applicati...&sku=C283-1202 Then you will need some fans for you computer, most cases come with fans in them, so that helps, but they are soo cheap it doesnt hurt to lower temps maybe 10 degrees C. so i would get a fan like this.http://www.tigerdirect.com/applicati...5&sku=V13-4200

Then A case, you can use whatever case, but everything needs to fit in there, but u can get really nice cases that keep everything not hot inside, old small cases will not cool enough. So go with one like so, http://www.tigerdirect.com/applicati...&sku=A406-1102 it comes with fans inside all ready to go, to get everything going..

After that all you need is to install any 64 bit operating system, so like xp 64 bit, vista if u like it 64 bit, or upgrade to windows 7 64 bit.. just make sure you have 64 bit or it will not see anymore than 4 gigs of memory which is bad...

Thats all hope that helps