If you have a Nexus one phone then you can download the official version of Android 2.2 Froyo now. However the installation has to be done manually as an AIR update is not available. If you own a Nexus One with a non-rooted stock ERE27 system the go and download in the following link,
http://android.clients.google.com/packages/passion/signed-passion-FRF50-from-ERE27.1e519a24.zip
If you do not have a non-rooted stock ERE27 system Nexus then no worries at all. Here is the link, from which you can download and install,
http://www.mediafire.com/?qt0hfogmuwt
How to install?
Download the zip file and upload in on your SD card.
Rename it to update.zip
Press Power on with Volume down held
Again press power and volume up this time.
You will see a warning triangle icon appearing on the screen, click ‘apply update.zip’ at that time.
Your Nexus One is updates with Android 2.2 Froyo [More]