Most iPAQ models come with an iPAQUtil.dll, whose usefulness varies among
models. It used to be you could get the "SDK" (basically iPAQUtil.h and
some documentation) for free from HP, but now I see they charge you $200 for
this privilege. Most of these versions include functions relating to
bluetooth control, including radio-on/off, but unfortunately not all the
implementations actually work. I think you'll just have to try it on your
system to see. You can probably look at the /exports with dumpbin to see
the calls you'd need and skip the $200.