I had a few questions about the actual purchasing process for the Menace of the Underdark expansion, so figured I'd post this faq including those questions. Keep in mind that this is really just some questions about the ordering itself. There is another faq here Tolero put up for other questions regarding the expansion.

When purchasing the Menace of the Underdark, why do I need to create a new account? Don’t I already have a Turbine account?
The distribution of the expansion is actually being done by a company called Digital River. They ask for an email and password to process the purchase. It is completely separate from your Turbine account. Once that is done, you will be able to purchase the Menace of the Underdark.

What is the ClickandBuy option? Does that mean it will use my credit card so I can then click and buy the expansion?
ClickandBuy is actually a company that does internet transactions, similar to PayPal. If you want to just use your credit card, make sure the first option, Credit Card, is the one selected. When you click on continue, it will use your credit card as the payment option.

Why is the quantity higher than I want it to be?
When you leave or reload the order form, it will increment by one each time. To update the quantity, you change the number to the one you want, then click on the refresh button directly under the quantity. This will update the page with the correct amount, and update the price on the right hand side. Once you have the quantity you want, go right ahead and click Check Out!