I'm also looking for a way to do this. Any ideas using the Nvidia or ATI SDK maybe?
Judging from results of google search, nvidia provides API for overclocking their GPUs, and there are some ATI tools available as well (though ATI tools look "unofficial"). However, there's no cross-platform API, and settings are probably extremely GPU-specific.
I'd strongly recommend to avoid overclocking GPU, becuase it'll be easy to fry or permanently damage it. To be fair, last cards I had were relatively resitant to overheating - one GF8400GS worked for a month with broken cooler without noticeable permanent damage. Of course, rendering scenes that used pixel shaders (while cooler was still broken) has been consistently causing surrealistic artifacts (in 3d apps) and corruption of desktop icons (on windows desktop), and system freezes - until cooler has been replaced.
So I'd recommend to avoid modifying any GPU settings (power/clock/whatever). If you're unhappy about power consumption, using different GPU might be a better idea. Radion 9000 is quite old, so it is possible that there are some newer budget cards that have more features and drain less power.