Good news, Bad news.
Good News:
On a standard CE system, SetSystemPowerState should do the trick (in pm.h)
Bad News:
PPC and SP might use a completely different power setup becuase all of the "standard" CE components are presented as "samples" for OEMs to override if they choose. So it might be there, it might not.
Good luck.
edit: cleanup errant UBB tag.