I like Powerstrip; It's effective, and has some display settings for when I play DVDs.
As for the limits to overclocking the Radeon 64mb ViVo, if it's an older Retail card (clocked default to 184/184), then you should be able to get up past 200/200 with little problem. The core limit seems to be around 220-230mhz for those, and the ram around 210mhz. Recently, a stealth improvement was made to the Retail Radeon 64mb ViVo, with the addition of 5ns ram (down from 5.5ns ram) and an increased clock speed of 198/198. Some of those have clocked past 250mhz core (highest I've seen was over 270), and the memory past 230mhz.