Technically, you cannot.
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).
Pasted from <http://onecare.live.com/standard/en-us/faq.htm>
Now, as long as your language is supported - that is the operating system language, you can use the unsupported, not sanctioned by Microsoft workaround to activate your subscription. At the end of 12 months, if OneCare is still not available in our country, then you will need to repeat the process below or a variation of it to renew with a product key.
Create a new LiveID with a US (or other country on the above list) address. Contact a trusted friend in the country you used to create your LiveID and provide that person with the LiveID, Password, and a OneCare product key from the retail box. Have them log in with the LiveID at http://onecare.live.com/activate and use the option to activate with a token using the product key from inside the retail box. They will not be installing OneCare and cannot use the key again.
Once that has been completed, change the password on the LiveID. (You can only trust people so far...) Then open OneCare on your PC and activate it with the LiveID used to create the subscription. Note that you can use a friend in any country where OneCare is available for sale per the above list. Reinstalls and installs to the 2nd and 3rd PC do not perform the check for IP and language (at this time, at least), so you won't need to repeat the process again.
I will remind you that the above is not an approved workaround and the process may cease working at any time.
-steve
