Power

You can power your Palm handheld from your automobile using:

Belkin makes a Y-cable for Palm handhelds which have a universal connector (Part # F8P3101). The serial connector of the Y-cable is used to connect to the OBD-II interface. The USB connector of the Y-cable is used to supply power to the Palm handheld.
 

PalmOne makes a recharging HotSync USB cable. Use the cigarette lighter adapter with the Belkin cable above (instead of the included USB-only cable). If your cigarette lighter provides "switched" power, then the Palm will automatically power on whenever you start your car.
 

GPS

Mapopolis is an excellent GPS navigational aid. Use both OBD Gauge and Mapopolis by connecting the HotSync cable of the Palm to a serial switch. The serial switch allows you to select either the OBD-II interface for OBD Gauge or a GPS for Mapopolis. You can construct a serial switch using a DPDT toggle to switch the RX and TX serial lines. I use this configuration in my own car with a Palm Tungsten T2 and the power connection shown above. I highly recommend the Tungsten T2 for its transflective display, compact size, and  sound capability (used by Mapopolis to give voice navigation directions).
 

Bluetooth

Socket Bluetooth Serial Adapter allows a Palm with built-in Bluetooth (such as the Tungsten T2 or T3) to connect wirelessly.