This subject was covered pretty comprehensively yesterday!
The difference between a Credit and a Debit cards is pretty simple and obvious.
Money used to purchase an item using a Credit Card is credited from an account held by the card company (Visa, Mastercard etc) on behalf of the client. Purchases are "credited" to the client up to a pre-arranged limit.
Money drawn on a Debit Card is taken (debited) from a bank account held in the client's name. Should there be insufficient funds in the bank account at the time of purchase, the request will obviously be refused. A Debit Card is in essence, a plastic cheque.
Many (the majority) of companies will NOT accept pre-orders on a Debit Card simply because they have no idea if sufficient funds will be in the account when the payment is due. However, some companies overcome this problem by withdrawing the remittence before the pre-ordered item is available.