The Samsung Galaxy S runs an older version of Android 2.1. From what we have heard, it isn't due to be updated to Android 2.2 until later this year although an Android 2.2 firmware has been leaked and made available to install now.
The Samsung Galaxy S Android 2.2 firmware is a test version which is important to note here. When we say test, we mean that a few features might not work and it might not be stable, hence it being a test version.
Full instructions have been provided to get the firmware going. If you prefer to wait for the official version of 2.2 Froyo then from what we have heard, the OS will be launching in September.
Some of the problems already spotted with the test version show that it slows down a little while multitasking.
Full install details can be found here.
Via: GSM Arena