can't activate iphone 5 or recover it

I got my unlocked iphone 5 today in the mail but it was too late in the day to get a nano sim card from my phone company so I decided to see if I could activate by just restoring my old iphone's setting since it doesn't let me use it in any other way..

Now I try to sync my iphone and it tells me i need the newer version of itunes and after noticing that I do have the latest version for my mac and that I can't upgrade to the newer itunes. Ok, so I don't know what to do, I am running a Macbook with intel core 2 Duo 2.4 GHz and 2GB of ram OS X 10.5.8.

Is there any way of being able to use itunes on my phone without upgrading my OS? I wanted to replace my computer very soon, so i don't feel like shelling out $40(I'm not in the US) for a computer I'm getting rid of in a few months and what wouldn't even be the latest version of the OS since apparently I can't run Mountain Lion unless I upgrade to 10.6.8 first...

What options do I have? Keep i mind I want to re-store my iphone. I do have a windows Vista machine, is there a way to "pass on" my back up? I'm sure I can actually run the latest version of itunes there since only on mac do they cut you off so harshly after 4 years, I don't expect computers to last me forever but it's a bit ridiculous.