For people with stock Nexus One, I would advise to just wait for Froyo update rolls out. (but you can also install it too if you really want it NOW.)
Here’s simple step on how to install Froyo Android 2.2 on your Nexus One:
- Free Download the Froyo Android 2.2 image and radio files. – here
- Put the whole zip file in the root directory of your Nexus One’s SD card.
- Reboot the phone while holding down the trackball button.
- Go to Fastboot then Recovery.
- (Optional) Back up your old ROM using Nandroid.
- Wipe to factory and also wipe dalvic cache.
- Install the new zip file.
- Enjoy the new Froyo Android 2.2!