Disclaimer: Backup your phone data and do it at your own risk, this can brick your phone.
Rooting unleashes the enormous power available with Samsung Galaxy S (SGS)’s super hardware, but sadly there are no official application to do that. Also, there are many applications which are pain in wrong place to get a rooted SGS. Luckily, I tested an android app ‘z4root’ which is in my opinion the easiest way to get your SGS (with Froyo, android 2.2) rooted.
Follow the given below instructions for rooting your SGS. You need to know how to transfer files from your computer to SGS; if you use Windows OS you can download latest version of Kies from official site of SGS and use that for transferring files. In case you are using MacOS, you can connect your SGS as external usb drive and transfer files.
1. Go to Settings>> Applications and check on “Unknown Sources”. This will allow you to install non-android market applications.
2. Now Download z4root from this link.. (remember this app is not available in android market), save the apk file on computer and transfer it to your phone memore/external card.
3. Locate the apk file using file manager “My Files’ on your SGS and install z4root.apk file.
4. After installation launch the application and select “Root” option. And you are done.
This has worked pretty nicely for me on My SGS running froyo.