Emmo 73~ Welcome to the DISboards!
I'll try to answer some of your questions:
You can buy Disney Dollars (DD) at the
Disney Store. Not sure about in the parks....
I don't think that you can "cash" them in. I know that when we were in WDW in May, we used them to buy food and if there was any change leftover, we got the change in cash.
We have purchased them at the Disney Store with a Visa debit card before. I have read somewhere that you can not purchase them online because they are considered "money" and Disney doesn't want the responsibility of sending "money" thorugh the mail.
To my knowledge, DDs do not expire.
If you need additional information, check these boards through the search function (if it is enabled), and you can always call your local Disney store with questions.
Hope that helps and again, welcome to the DISboards!
