OneCare is still not for everyone as I also found out before.
The only payment methods online that are available are MasterCard, Visa and American Express. You must be in the same country as where your credit card is from to get this work or you might get this message:
"We can't authorize the payment method. Please make sure the information is correct, or use another payment method. If you continue to get this message, please contact your financial institution."
According to the OneCare FAQ:
In which countries and languages is Windows Live OneCare available?
The Windows Live OneCare subscription service is available in the following countries and languages: Australia (English), Austria (German), Belgium (Dutch, French), Canada (English, French), France (French), Germany (German), Ireland (English), Italy (Italian), Japan (Japanese), Mexico (Spanish), Netherlands (Dutch), New Zealand (English), Singapore (English), Spain (Spanish), Switzerland (French, German), United Kingdom (English), United States (English, Spanish).
There is an unofficial workaround described if you have someone you really trust in any of these countries.