How reverse an iPhone software update

Hi,

I have an old Mac (PowerPC G4 with only 700Mhz) running Ox 10.4.11. It have iTunes version 9.2.1 (4)

I stupidly updated my iPhone 3GS to IOS 4.3.3 (8J2). This will only sync with the newer iTunes version 10.

As my Mac is too old to support OX 10.5 or 10.6, I can't upgrade to iTunes 10.

This means that I cannot synch itunes or copy music from my Mac itunes to my iPhone.

So,

How can I reverse an upgrade -  WITHOUT Losing all the music, etc, that I have on my iPhone?

(Note - I have more stuff on my 30 GB iphone than my 40GB Mac can handle....)

Any suggestions welcome.

Thanks.

Max