GPU-Z, if it does not display (which happens quite often), try RivaTuner.
Riva Tuner is no longer updated and has basically been changed into MSI Afterburner. If anything is going to show the VRM temps I'd think it would be that. It should have actually come with the card I believe.
The GTX 460 has nothing at all back there to monitor vrm temps. Only the core on these cards has a thermal sensor and the only way to check temps is by infra red camera or thermal probe. It is best to apply any form of cooling possible as the vast majority of the gtx 460 cards out there either don't have enough cooling or nothing at all. 150-200w with nothing at all is basically a suicide card. This is not like other cards out there like the 6800gt/ultra that had a digital power vrm or many mid range and high end ati cards that do make use of thermal sensors ect.