Net Render is great for animations, somewhat more work for stills (but still faster). You have to be aware that different CPU’s with different FPU’s should not be mixed. From the manual….
“Inaccurate Calculations
One common feature of heterogeneous (unlike) networks is that they usually involve computers with FPUs (floating point units) that work to varying degrees of mathematical accuracy. This can lead to rendering inconsistencies such as particle streams (as with the previous CINEMA 4D particle system) or with Clothilde / HAIR being calculated in very different positions on different machines. Nobody can predict when these inaccuracies will arise, nor will anyone be able to tell you how severe the deviations will be.
However, CINEMA 4D solves this problem (at least with particles) by allowing you to bake the particle stream prior to rendering. This only works when using CINEMA 4D’s own particle system (not for Thinking Particles) or Clothilde / HAIR. Nevertheless, we recommend you always make a quick preview before commiting the final render.”
So with you having a PPC either it would be best to get PPC’s for a farm or use the PPC only as the net render server but not as a renderer and get a number of machines using the same chip to run the renders.
But the first thing I would do is to think about the PPC, assuming the 2.5Ghz quad you are probably getting Cinebench scores something like 2000 for CBSingle and 7000 CBMultiple. My 8-core 2.8 intel Mac gets 3200 CBSingle and 19000 for CBMultiple so you could (depending on what it is you are rendering) probably do better than chopping your render time in half. Otherwise, if you can get your hands on a number of G5 machines that would be the thing to do with Net Render.