I' recently got a copper tubing one from my local scrapyard for a tenner (damn good deal). It works superbly. It's not like a heatercore though ( which has a big space at each end and the water can 'choose' it's own tubes to pass through the rad), instead; It split into 3 tubes at the entry and they run back and forth all the way through it until the exit where they join up again. This obviously increases the resistance.
However, don't worry about the pump. This thing is the size of my computer case and yet my Eheim 1046 could push water though adequately. Though it wasn't great and I got a Eheim 1250 instead. Though the difference between the pumps wasn't as great as I had expected and that's 'cos the head pressure between them isn't as great as the flow rate difference.
Anyway, yeah, it's well worth it. You can have supremely quiet fans on it yet still get a massive overclock.
The ONLY downside is that it's so big you have to find a way to mount in on the side of your case.
I'd post pics, but my bro's digi-camera has no batteries...
There's no for sure way of knowing if it has copper tubes or not because the tubes always look silvery cos of the aluminium fins attached to them. Bizarrely, I've heard that if it's painted black (liek mine) it probably has copper tubes, and if it's silvery/grey, it porbably has aluminium tubes. This is not due to anything physics like, but simply the black ones tend to be older and in those days they used copper. Nowaday they mostly use aluminium.
You can of course just inspect the inlet and outlet tubes, but you can only do thay once you've hacked it out of whatever car you've found (assuming you're getting one from a scrapyard).
Hope that helps.