Last week, Google announced of rolling out the ability to users in 18 additional countries to purchase paid apps from Android Market. "For users to make a purchase of paid apps in these countries, they must have latest Android Market client, which we've started to make available as a self-update and should reach all users within next few days. This is a silent update; users will not see a notification and will not be prompted to do anything.
If you want to accelerate the self-update process, launch Android Market, navigate back to Home screen, and after 5-10 minutes, relaunch it," explained Google.
For more details, please refer to Help Center