Upgrading from iTunes 9 to ?? on OSX10.6

Hi Everyone,

I hope you guys can assist.

My wife got a brand new iPhone 4S. We are struggling to get her iMac to pick it up in itunes. Heres the detail,

- Mac OSX is 10.6 and iTunes is 9

- I then realized i need to upgrade the version of iTunes to at least 10.4 for it to pick up the Iphone 4S ( Correct??)

The thing is, I have been unable to install any older version of itunes, every installation gives me an error:

"The Installation failed

An unknown error occured

The Installer encountered an error that caused the installation to fail. contact the Softw Manuf for assistance."