Do the following steps to install froyo on your galaxy 3.

1.Download Odin Multi downloader .
2.Download any of the following 4 Firmwares.
      1.I5801BVJP9
      2.I5801BOJP6
      3.I5801ZFJPE 
      4.I5801BOJPC
(The Password of all the above Firmwares is samfirmware.com )

3.Download .OPS File.
4.A windows PC + samsung data cable.

5.You must install the latest kies version so that you have required drivers for samsung i5801 / i5800

6.Backup your contacts , data and apps as the process will wipe everything from your internal memory.

7. Take a note of your Firmware version by typing *#1234# incase your need to revert back later.

8. You don’t need to root your device to get this working.

9. IMP: HARD RESET YOUR PHONE . MAKE SURE U HAVE ALL YOUR DATA BACKED UP. THIS WILL MAKE SURE YOU DONT HAVE ANY ISSUES WHILE UPGRADE.


STEP 1

• Download all the above files listed above .
• Extract all the files in the separate folder , you will get the TAR files

STEP 2

• Open ODIN Downloader.
• SELECT Package, Auto Reboot and Protect Ops checkboxes.
• Select the Ops file that we have already downloaded
• Select the tar package that we have downloaded

NOW EXIT ODIN.

STEP 4.

• Turn OFF the Galaxy 3 and get your battery out and sum card as well.
• Reinsert The Battery and Press the following buttons together
• Home + Menu + Volume Down + Power

Step 5

• Now Connect your Phone with your PC using the ORIGINAL DATA cable and wait for windows to finish installing the hardware

• Once you get a prompt – ―the device is ready to use‖

• Start ODIN DOWNLOADER (make sure the settings are same as before) Your phone will now show up connected in Com Port)

STEP 6 

• (Final Step) CLICK START and wait for process to finish, once done your device will automatically reboot and will have Android 2.2 running on it. Enjoy!