How to update and install Android 2.2 ( Froyo) on your Smartphone
One of the key features of the Froyo Android 2.2 is that USB/WiFi tethering comes as default, meaning you no longer need to hack it to get it. Btw, it works flawlessly, Google did a great job of adding the tethering into native Android. For developers, the Android 2.2 platform is available as a downloadable component for the Android SDK. The downloadable platform includes a fully compliant Android library and system image, as well as a set of emulator skins, sample applications, and more.How to Install Froyo Android 2.2 on your Nexus One
Step 1: Download the rooted Android 2.2 Froyo (FRF50) from here
Step 2: Once Android Froyo 2.2 (FRF50) has been downloaded, copy it to the root of the SD card on your Nexus One.
Step 3: Once its done, power off the phone and enter the recovery mode by powering on while pressing the ̣€˜Home" button (trackball) and select "BOOTLOADER" ̣€“> "RECOVERY"
Step 4: This will result you to be rebooted into custom RA recovery mode. Now select ̣€˜Backup/Restore" from the front menu to do a backup.
Step 5: Okies! It is half way done. Now select the "Flash zip from sdcard" to flash your Nexus One with this latest rooted Android 2.2 Froyo FRF50 ROM.
Step 6: In the second last step of the process, you need to do a complete wipe by selecting the "Wipe" option as shown in the screenshot above.
Step 7: Yups its final step! Just reboot your Nexus One!8. Enjoy the new Froyo Android 2.2! Hurray
Source : B4tea.com