How to revert to older version of iTunes

I'm always apprehensive of updating iTunes to newer versions.

Just bought an iPhone 5 64GB and I'd like to sync it with music.

My older phone (32 GB 3GS) had complications when I first bought it, so I'd chosen never to update IT or my iTunes since.

The 3GS is still running on an older version (3.1.3 [7E18]) and it's been amazing through my 3 years of use.

The version of iTunes I'm running is 10.3.1 from back in 2011 (I believe) and I'm quite happy with it.

My iPods AND iPhone have given me no problems these past few years.

In order to sync my new phone, I'm expecting that iTunes will require the update.

So... Is there a way to SAVE my current version of iTunes (10.3.1) in case the current one is not to my liking?

I was hoping to save a copy of it to a USB key.

I'd also appreciate instruction on how to revert back to this older version if I need to later.

I'm using a MacBook Pro with Mac OS X Version 10.5.8

2.53 GHz Intel Core 2 Duo, 4 GB 1067 MHz DDR3

Thanks in advance, and have a Safe & Happy New Year!