how to install tomtom on htc touch diamond. usually TomTom Taster version was bundled with htc touch diamond device, you can install tomtom from the application CD.
1. Connect your device to your PC and ActiveSync via a USB connection.
2. Insert the Application CD in your CD/DVD ROM drive.
3. Execute the TomTom application.
4. Follow the onscreen instructions on your PC and wait untill it instructs to check any actions needed on the device to proceed with installation.
5. On the device choose whether to install TomTom to SD card or Device Memory.
6. …

HTC Touch diamond no gps signal problem and fix. when your HTC TOUCH diamond can’t detect any GPS signal. maybe there is some problem with GPS antenna. you can check : Is your device’s built-in GPS antenna covered by any material with metallic coating (e.g windshield, sticker etc)? These materials may interfere with your GPS signal reception. Since GPS signals from satellites often cannot pass through buildings, please test the GPS outdoors. if you are using an external GPS antenna, please make sure it is securely and properly connected …

you can use HTC TOUCH diamond GPS with installing TOMTOM gps application. you should download tomtom application, or download free google map for your HTC TOUCH phone.
How to use external GPS in HTC TOUCH diamond:
Launch the TomTom application, tap on the screen, and tap on Change Preferences, go to preferences screen 3 of 5, select Show GPS Status and select Configure. Select Other GPS NMEA and set the baud rate to 4800. Next, set COM port to COM4. Wait until it acquires a GPS signal and then tap done.