Hi, welcome to the forums!
1. They are treated the same. It
might help to have a store card if all you have is bank cards. It definitely helps to have a bank card if all you have are store cards. At any rate, they don't hurt.
2. I assume you're talking about being an authorized user (AU), where you weren't an original applicant, and you aren't responsible to the bank for the account. Yes, you'll get all the good and bad from the account, if it shows up on your reports. Not all AU accounts do. If you were a joint holder (NOT advised!), the account will be listed, and you will be responsible for it if the other person flakes out.
3. Are you talking about getting off the AU card? If so, yes. You can ask the cardholder to remove you, or you can call the bank yourself. Some banks want to hear from the cardholder. If you can't get anywhere in this manner, you can dispute with the credit bureaus as "not mine", although you should do this as a last resort. Disputing with the CRA's can open up all sorts of headaches.
If you haven't already, please read
Understanding Your FICO ® Score and
Credit Scoring 101 (at least the first post.)
These will give you the background knowledge you need to understand what you read here on the forums.
Message Edited by haulingthescoreup on 12-21-2009 03:40 PM
* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit?
FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007