how do i buy the update on vista!

I have windows vista, itunes 7.5 and a 8gb ipod touch on 1.1.3 and when i go onto the apple website to buy the upgrade it opens my itunes and im confronted with a page that talks about the 5 new apps but there is no buy button just a reminde me later! what is going on? and how can i fix it?

Get iTunes 7.6?

I think you need to update