Guys over samdroid have rooted Samsung Galaxy S running Android 2.1 successfully providing full access to its system files. The exploit provides a /system/bin/su from AOSP (that is, you can only use it from adb shell). Once you get the full root access to the file system of Galaxy S, you can modify the phone’s firmware and install third party apps, themes and custom ROMs.
You just need to flash the kernel for galaxy S i9000 with root. Your data or programs will not be deleted. Leshak, the guy behind the jailbreak suggest that experienced users should try this method as it is danderous and might brick you phone.

How to Root Samsung Galaxy S
Step 01 - Download: i9000_Kernel_LK9_01b3.7z. If you have problem with this Kernel, you can flash original Kernel from JF2
Step 02 - Unpack
Step 03 - Flash with Odin3 as PDA file
Via – Samdroid
