Ringtones option does not appear on itunes

I have a windows vista and I just got an iphone 2 weeks ago. I downloaded the new itunes 7.4.3.1 but when I open itunes and plug in my iphone, the new ringtones feature does not appear on my itunes. I tried installing the itunes 7.4.3.1 a couple of times. Still the ringtone feature does not appear. I have also authorized my computer and have signed in to itunes store.
Can someone please help me? I just want to buy some ringtones