This is a very simple guide to install Android 2.2.This will unroot your device, revert to stock, and update to FroYo.Download and unzip the original shipping Rom. (I unzipped it to the tools folder so I didn't have to type the full location in the cmd.exe)Plug in your Nexus One to your computer via USB.Open a Command Prompt on your computerType adb reboot bootloader. This will boot into the bootloader.Confirm fastboot connection by typing fastboot devices.Erase your Userdata by typing fastboot erase userdata.Erase your Cache by typing fastboot erase cache.(If step 6 and 7 do not work you can alternately do a factory data wipe within Android. Settings/Privacy/Factory Data Reset)Go to the directory where you stored your unzipped image file.Type fastboot flash userdata userdata.imgType fastboot flash boot boot.imgType fastboot flash system system.imgType fastboot flash recovery recovery.imgFastboot rebootBoot into Android > Settings > About > Update > Download and Install (This should be update-1)Download and copy the following zip to your SD card, and rename it update.zipReboot in to the recovery. Power+Trackball > Bootloader > RecoveryPress Vol Up+PowerApply update.zipFinish and reboot.Copy the following to your SD card and name it update.zipReboot in to the recovery. Power+Trackball > Bootloader > RecoveryPress Vol Up+PowerApply update.zipEnjoy----------------------------------------Football for the Original Shipping ROM link.RomRAID for the ERE27 Link.Gu1Dry for FroYo Link.