If you want your own account, you need to buy a separate copy of the game.
You can both share the same computer, and even the same install, but the game comes with registration codes that you use to create the account. You can only create one account per copy of the game you buy, and only one person at a time can play per $13/month that you pay.
____________________________Pergatory (Asura, Kupo LS) WHM99 ~ SMN99 ~ DRK99 "If you want to know me, look inside your heart." -Lao Tzu