Focituner, I'd head off to any electical / electronic place (not Radio Shack, they won't have it)and look for a 16 or 18v (can't remember which is the std.) 1farad cap. If you wanna get a name brand one, it's all the same sh**, just a different pile. 1 farad is 1 farad. As for where to put it, they usually end up out by the amps because that's where the power cables are getting split up anyway. It's not a big deal if you wanna put it out in the engine bay or somewhere remote, but just remember that like any other high current application, the longer the cables, the fatter the cables. If you wanna put it near the amps, (probably the best idea) 8ga cable is fine, as long as the leads between the cap and the power cable are no more than a few feet long.
Just incase you're not familiar with how it should be wired, you wanna run it in parallel with the power cables, ie. positive lead of the cap to the positive power cable, negative lead of the cap to the negative power cable (or ground). Oh, charging/discharging. Grab any 12v device, a light bulb works great. When you're all set to hook this baby up, hook up one of the leads to the cap, and connect (temporarily) the light bulb between the other terminal of the cap, and the lead that should go there. The light will come on, and slowly dim until it goes out. When the light's out, it means the cap is charged, and you can safely remove the light and connect the other lead to the cap. If you just hook it up, you'll get a nice big spark, and probably take out the fuse for your power cable. If you ever need to disconnect the battery cables, you'll need to re-charge the cap before you reconnect the battery cables, or again you'll get fireworks. I always leave a note in the car whenever it goes into the shop, so they know if they need to disconnect the battery to work on the car. If you need to remove the cap, you'll probably want to discharge it. Just remove the power leads, and take your handy-dandy light bulb across the two terminals. Again, light will come on, and then dim until the it is completely discharged. It'd be an awfull suprise to stick your fingers across that thing when it's got a full charge.
Have fun!