How can I upgrade the spec of my mac from version 10.3.9 to something that will allow me to install my iphone?

[Pennies]

Can anyone help? I have bought a lovely shiny new iphone which DH and I are pathetically excited about and it won't let me install it as my mac runs on an old version.

thanks, rg, I'm getting VERY fed up with the 7 yr old Dell PC that dd uses, I think it's time to upgrade!