How can you know about your membership?
On RuneScape, go to the main page and click on:
Account-->Account Information -->
And then you log in and you look at your information. From the Account Information page, however, you can find out a lot about your account.
I don't think you can buy club penguin membership for a week, as far as I know when i played it it was only used for months of memberships and 5 euro/dollars/pounds. But i quit Club penguin because it is babyish, for me. I am 15 and you know haha. So, I dont think you can get membership for a week, I am sorry :-)