Need scripting help

Hi guys I've been playing around with bitcoin mining for about a month now got my self an asic usb errupter to toy with but ive got 6 computers in my house for my family and there on pretty much 24/7 downloading stuff, I've got for kids and myself and my wife, the problem is they all have got NVIDIA GPUs, and ive done quite a bit of reading and everyone says there pretty much useless for mining but still there not under load all the time so its computer power that i see and its not being used so a little is better than none correct. I was hopping someone could help me out or point me in the wright direction the cards all support OPENCL but ive been doing some reading and people say CUDA is better for NVIDIA is this correct i would like a definitive answer.

What I need help on
I need a script for either BFGMiner OR CGMINER OR RPCMINER(CUDA) that limits the use of the miner to 20% at all times on the GPU and OR CPU(for a extra boost)
I need the script to run on the different cards without modification to it (this is the bit Im having problems with).
Also if I need to use RPCMINER(CUDA) i need a new pool that doesnt need to run a proxy.

Any help on this issue would be greatly appreciated.

Regards
Adam M