You're going to need to do some research. Look at the sticky's at the top of the page as they contain a ton of information. Here's a basic run down to planning your system....
Decide what you want to cool. It sounds like you want a CPU and a GPU, so you'll need to determine how many watts of heat those chips are going to put out. I don't have the links handy with me right now, but somebody will chime in here soon I'm sure and point to you where to find out that exact information. For preliminary planning purposes you could probably go with something like 200 watts for an overclocked i7 900 and 300 for a GTX 580.
Then you should research some fans because you have to know what fan speed you can tolerate before you can select radiators. You can look at some fan reviews done by Martin
here and
here. Have a look at those fan reviews and identify some fans you might be interested in. Then either look at the videos provided by Martin or check out
this guys youtube channel. He's got video of a lot of fans running from dead stop to full speed, so you'll know how loud they'll be under a fan controller or full speed. This is not a perfect way to determine tolerance because often times fans are louder in videos than they are enclosed in your case, but it will certainly give you an idea.
Once you know how much heat you need to cool and how much fan speed you can deal with it's pretty simple to determine the best radiator for you and how much of it you'll need. Go to
Skinnee's Lab and
Martin's Liquid Lab and read some radiator reviews. If you find the radiator sections there will be radiator comparisons for a given size. Look at those reviews and there should be graphs that show watts of heat dissipated on the Y axis and fan speed on the X axis. The graph will either have multiple lines on it for different radiators at a given temp delta, or it will have multiple lines on it for various temp deltas on the same radiator. Find your identified fan speed and find the best radiator for you. If there's several that are comparable go for looks or price or find individual reviews about build quality, etc. Radiator cooling capability is proportional to size, so there's a couple ways to derive cooling capability for any radiator of the same family that is in the review. For example, find the area of the radiator (240x120mm=28800 mm^2) and divide the watts cooled by the area (300 watts/28800 mm^2 =0.0104 watts dissipated per mm^2). You now know how many watts dissipated per mm^2, so you can determine how many square millimeters it takes to cool your heat load. For 500 watts it would be 500/0.0104 = 48706 mm^2 required with that particular radiator model. Then you just divide that by the fan size you want to use. For 120mm fans it would be 48706 mm^2/120mm = 405 mm. This would mean for this particular setup you'd want a 420mm radiator of that model because an ideal size would be 405 but 420 is as close as you can get. This is a purely hypothetical example. Another quick way to know how much a radiator can cool is just multiply by the size factor. For example, a 360 is 1.5 times the size of a 240 so just multiply the 240 cooling capability by 1.5 and that's your 360 cooling capability for same series radiators.
For the case, you're going to struggle with that case. I'm guessing it's going to have to be mostly external. Search the internet for build logs of water cooled systems with your particular case and see if anyone has been able to do much with it, but this may be a source of struggle. Mid towers just aren't made for internal water cooling. Full towers aren't made very well for it for that matter. Super towers are starting to fit pretty big systems inside.
That gives you plenty of research to do now. Read the sticky's on the front page to get a basic idea of water cooling. Then go through the steps I've outline above to help you select your radiator/fan set up. You can decide pump, fittings, tubing, res, etc. later because those choices are based mostly on preference and not so much how you want the system to perform. I.e. you're going to choose the same of those pieces whether you build a high speed fan high fpi radiator set up or low speed fan low fpi radiator set up.
