The popular tweaking utility, Tweaks2k2, has just been updated with 2 new tweaks specific to the iPAQ hx4700. The first one allows you to control whether the power LED is on or off; the second lets you make the power LED blink. This is in addition to some previous hacks that allow you to control other LEDs (such as the Bluetooth one).
With the 30% discount being offered on the site, the price for Tweaks2K2 is $10.85 USD. A trial version is also available (for first time users only).