I had a similar problem with my 9600PRO card. If I overclock it past 2.42Ghz, and get like 2.5Ghz, if I leave my default voltage in BIOS at 1.5V for the video card, I'd get booted out of games, and 3DMark03 & 01SE both keep crashing to the desktop after either a few seconds of running or just a few rounds.
But when I increased the voltage to 1.7v or 1.6v (I forget which), it ran stable... Someone told me increasing the voltage in the BIOS only fries the video card and really does nothing, but who knows? I switched to a 9800SE since, but I've swapped out my Ti4200 for the 9600PRO now on my first system. I haven't tested overclocking the card and stuff yet... but will soon. So far, it runs stable on stock speeds.
EDIT: Oh, and my +12v rails are 11.67 as shown in MBM. But I've tried both a 380W Antec True Power and 430W Antec True Power as well, and they are both the same readings. I do, however, have 6 total case fans running hehe. All the other readings are closer to the listed voltage.