Turn your desire off
Hold the back button and turn your desire on
When you are at the white screen, make sure BOOTLOADER is selected and press the power button
Wait a few seconds then press volume down to select RECOVERY and press the power button again
When you are at the screen with the red triangle and the phone, plug in the usb cable
Run the recovery-windows.bat script from modaco r5 root pack
When the recovery menu appears select 'Flash zip from sdcard'
Select the radio zip file and press the trackerball to confirm
Press the trackerball over 'Reboot system now'
When the radio image has finished being written unplug the usb cable
The phone will reboot a couple of times and then return to a normal state with your new radio