[Nexus One Q&A, Help & Troubleshooting] DarsVaeda:
Sure.

First of all I lost all data that was not saved remotely. Like SMS or application data from applications that do not remotely store data. Keep that in mind! But it's worth it.

I backup SMS to my google account anyway and delete them after some time from my phone, so I was fine with that.

As far as I know now you do not void your warranty if you root with "SuperOneClick". The root will also be gone after you flashed the rom. On my phone there is only a program called "superuser" left, but it's not usable since the phone is not rooted anymore.

Step by step:

before get all of this:

- get and install the USB Android drivers on your WindowsOS explained here (and download): http://developer.android.com/sdk/win-usb.html

- install "RomManager" from the market on your phone

- get "SuperOneClick" here: http://xdaforums.com/showthread.php?t=803682

- get the Gingerbread Stock ROM: http://xdaforums.com/showthread.php?t=968396

- rename the stock rom to "root.zip" and place it on the SD-Card, top level

1. on your phone goto Settings -> Applications -> Development -> check "USB debugging"

2. connect phone with USB to your Windows machine (drivers above should be installed and Windows should recognize the phone)

3. fire up SuperOneClick and click "root", wait until it tells you it wants to run a test

3a. if it fails to root the first time, just hit root again (I had to do it, after second try it worked)

4. restart the phone after it is rooted

5. back in Android start RomManager

6. in RomManager flash a custom recovery, I took the one at the bottom (something with alternative recovery, second last entry)

6a. it might want you to install additional software, allow it

6b. it will ask you for rights, allow them

7. after the flash is finished boot into the recovery (second entry from top of rommanager)

8. in the custom recovery navigate to the point where you can apply an update with a zip file (in the one i took it was the second entry I guess)

9. after you choose the entry you can choose the zip, choose the "root.zip" and apply

10. now the installation should start with verifying and then actually applying the rom

11. restart the phone

11a. if you are now stuck in the start animation (the one with that floating x-thing) and it does not go on you have to reset all you data (factory reset)

11b. power off the phone and start it with pressing the power button and volume down

11c. a screen appears, navigate to "recovery" and hit the power button (you have to wait till it loads something, then you can press that)

11d. in the new screen there should be an option called factory reset, if not it is like "wipe all data" -> that's when you loose all your data (I had to do it)

11e. reboot the phone

12. Gingerbread should boot now

Feel free to ask any questions if you have. Hopefully I can help.

I did not use the stock rom directly, guess that saves you one step.

If it does not work, but I guess so you have to do the same as above but install this rom first:

http://dl4.htc.com/RomCode/Source_and_Binaries/signed-passion-img-FRG83_0923.zip

After you installed it boot the phone and check if the version is correct: Settings -> about phone.

If so get the Gingerbread update (http://android.clients.google.com/p...signed-passion-GRI40-from-FRG83G.81304b2d.zip) and place it on the SD-card as "update.zip".

Boot to the recovery, same steps as the factory reset. There will be an option "apply update.zip". Use that and after it you will also have Gingerbread.