Hi Mitch,
Sorry for the delay, I was enjoying a rare bit of sunshine here in the UK and totally forgot about this thread.
To manually update your phone you will need to visit
SamMobile Firmware Page and register for a free account. The firmware file for you to download is I9000XWJVN (third one down from the top).
From the same site you can download Odin, which is the software needed for flashing your Galaxy S.
Once you have downloaded all necessary files, unzip the firmware folder and put your phone into download mode. To do this, switch the phone off until it vibrates then press and hold Volume down + Home + Power (in that order) until the screen shows the Android robot in a yellow triangle.
Now, launch Odin and click PDA and navigate to the unzipped folder you've just downloaded and select the CODE file.
Next, click Phone and select the Modem file.
Lastly, click CSC and select the CSC file.
Now, connect your phone to the PC via USB and wait for Odin to connect with it. You will see a pane on the left hand side where it will say Added and above there will be a box with the word COM.xx (x represents a number and may be different to what appears on mine).
Now, click start and wait for Odin to complete the flashing process. It shouldn't take too long but once it's done, the phone will reboot and take longer to boot up than normal. Leave it connected until it has rebooted and your good to go.
If something goes wrong during the flash and you end up with what you think may be a bricked phone just repeat the process and try again. My first attempt at flashing went wrong because I got my PDA and Phone mixed up but a second attempt was successful.
According to Optus the latest firmware is 2.3.3 but the new 2.3.6 is scheduled for release in early June.
Good luck
Ray.