I just rooted my LG Optimus One P500 with Froyo 2.2 with a one-click application named Gingerbreak.
1. First of all, you must download the Gingerbreak installation file from the XDA forums. Here’s the link: gingerbreak-v1.20.apk
(Ignore the message that says it’s incompatible)
2. Open OI File Manager and go to mnt/sdcard/download.
3. Open gingerbreak-v1.20.apk from your list of downloaded files to install the application.
Enable USB Debugging
4. Go to Settings and then select Applications. Click Development and select the USB debugging checkbox.
5. Open the Gingerbreak app and click Root Device. Your phone will reboot automatically when the rooting is complete. This will take a little longer than your usual boot up time but don’t panic!
Finally, check for a new app named Superuser in your phone to confirm that your phone has been rooted.
Don’t worry if your SD Card has other stuff on it. Mine did too but nothing happened to them.
Ensure that your phone has enough battery charge to go through with this. Interruptions during rooting can cause problems.
If for some reason the procedure does not work, then turn your phone off and turn it back on before retrying.
If the app does not work,check if you have installed the app on the Phone memory and not in the SD card. Move the app to Phone if it’s on the SD Card.
You can now kick some serious ass with your rooted device!