Here is a link to the article that tells you step by step on Creating an iTunes Store, App Store, iBookstore, and Mac App Store account without a credit card: http://support.apple.com/kb/HT2534
Here is a link to the article on changing your account information: http://support.apple.com/kb/HT1918
I don't know weather these articles will be of help to you in Afghanistan.
guys here's what you need to do...
In the Terms and Conditions part of the sign up process, you need to CHANGE COUNTRY OF BILLING ADDRESS to USA.
and after that, you just need to fill up the form and the NONE option will be available.
I just did that a few minutes ago. I hope you'd be able to also. *wink*
You can indeed still sign up without a credit card using the none method.
1. Open iTunes and make sure you are not signed into an Apple ID.
2. Click on iTunes Store in the left column.
3. Click on App Store across the top row.
4. Pick any free app to download and install.
You will be prompted to enter an Apple ID, instead choose to create a new one. You will now be presented with the option for "None" on the billing page. You must still enter a billing address, but no credit card will be needed.