Heat pipes are now used in heat sinks very effectively these days. I was a little sceptical to the efficacy of heat pipes till I realised that most laptops use this tech to keep the CPU cool, and comparison tests have shown that its much more efficient thatn without it.
How it works:
Basically, it just provides a heat conducting rod with low thermal resistance. Therefore, its efficacy is reduced the longer it is. Its like stretching a metal rod over a fire, a short one you'd burn your hand pretty fast, a long one you might not feel anything at all for a long time.
Also, I doubt you'd want to insulate the section of the pipe in the case, you'd more probably insulate the whole thing. At least you'd insulate the bit outside the case, so that the cold temps from your ice bath will reach the PC. But you want it to reach the CPU, so you'd insulate the whole bit. And you'd need a really thick heatpipe....
I won't suggest you do that.
A better solution? Water cooling, and run your radiator through that ice bath of yours
