No es tan secillo, no se hace por fashtool, primero tienes que flashear el kernel ya que usa su proprio kernel (via fastboot), luego la rom via recovery...
Alli en XDA lo explican..
Código:
HOWTO FLASH ROM
to flash cm7 rom you have to take 3 steps (after unpacking the 7z archive)
step 1 - copy update.zip to sdcard
step 2 - flash new kernel (always use the kernel provided in CM7 / it is incompatible with stock ROM)
ON PC - run fastboot flash boot boot.img (an black window will open and will stay open untill kernel is flashed)
ON PHONE - put phone in fastboot mode (power off then press lower right key and plug usb cable) and phone LED will light BLUE
step 3 - when phone is booting (first 5 seconds) press volume key several times to enter recovery and choose apply update from sdcard
WARNING - if you used another rom (stock or custom) you have to wipe data or device will not boot
