Are you sure rivatuner can do it? I recently uninstalled it and I don't think it had that option, but if it does I'll go get it again. Btw that same site mentions that BIOS's that don't have a voltage adjustment section for GPU's is probably an indication that the motherboard doesn't support voltage changes.
Hmm I'll have to figure out a way to make my card get its own line, there are only 4 power lines, each are chained so it's 2 connectors on each, and I have 2Hdd's and a dvdrw so all are taken.
I think I'll try running it with the DVDrw as it's always idle and barely drawing any power, that is, assuming the power to my gfx card is chained to one of the HD's and not my DVDrw.

Will crack open the PC tomorrow and try this, thanks.