Looking at your profile it looks like you're based in the UK? If so you should have no problem running the Samsung's European JPO release of the Galaxy S Froyo software that went out to unbranded UK Galaxy S's a few weeks ago. As this is an Official Samsung release there's no need to root to apply it, you just need to trick Samsung's software into installing it for you.
To start with I'll make the assumption that you have no problems running the Kies software, that it recognizes your phone when you plug it in, and that you get a "You are already running the latest release" message when you click the Firmware Upgrade link. (this is a big set of assumptions given the quality of Kies, if any of these aren't true, then you need to get Kies working properly before going further).
This post on Vodafone UK's Galaxy S forums lays out the steps Samsung Galaxy S - Froyo Update (Android 2.2) (reply 113). I'll summarise them below as Vodafone are about to upgrade their forums to new software, so I have no idea if the post will survive, or the link will still work in a week or two's time, credit to "ado28" for these instructions.
First of all you need to go into
regedit and do some minor alterations
to the registry.
Do not update Kies! If you do then I
think this tweak won’t work! The Kies
version I used was 22.214.171.12424_74 but
I fooled it into thinking it was the
Step by step guide
Back up everything you wish to keep, including Apps, phone numbers,
Text messages etc because we're going
to wipe your phone clean before we
Go to Settings – Privacy – FACTORY DATA RESET and click. Follow the
prompts and then let it wipe your
Now you have a bare naked phone again and can proceed onto the next
Open up Kies and leave running
Open Regedit by clicking on Start – Run – then type in
regedit and press
Scroll down to Kies and look for “
Localver” see pic
Change your Localver code to
Now go to your Device DB folder and change your settings to these:
DEVCONINFO"="" Delete the writing
in this box and leave blank.
- Now go back into Kies and click "Update firmware"
This will now allow everyone who has
JPA on their handset with the product
code XEE to be replaced with JPO and
the product code XEU which is for the
UK. Once you have successfully updated
then allow the phone to boot up. Once
booted up you will now need to go back
into your settings and change your
product code to XEU. To do this open
your keypad and type in
IMEI# and now you will be back to
having a lovely wee choice of product
codes to enter. Choose
install. The phone will reboot and you
will now officially be on JPO with the
correct product code XEU!
Please note that by doing any update
on your phone could cause it to brick
itself. The guide I have written
worked perfect for me however I can’t
be held responsible if your phone
bricks itself. To be safe always try
the 3 button recovery method first
before you update and also doing a
factory reset first usually ensures a
smooth installation of new firmware.
Extra note on Kies: as stated above, this doesn't work with the latest version of Kies. If you need an older version of Kies then this version should allow you to do this (according to XDA): Kies version 126.96.36.19993_82.
If you do end up uninstalling and reinstalling Kies and find that it doesn't detect your phone any more, then first thing to try is clicking the menu icon in the top-left corner of Kies and selecting the "install drivers" option.