No holds. You have to purchase the ticket, then use the 'customer first' policy to get a (no-fee) refund.

From NW's site :

# Will I be able to hold my reservation if I want to explore other travel options?

If you purchase your ticket at the time you make your reservation, you can secure your ticket, the fare you've been quoted and a guarantee for a full refund without penalty fees if you cancel your reservation by the end of the next day (midnight Central Standard Time). Customers First refund can be requested on nwa.com. If you don't cancel the reservation, however, you will not receive a refund unless you have purchased a fully refundable fare. From nwa.com home page, select `View Reservations' or click here to go to `View Reservations & E-Ticket Details' page. Provide passenger last name and confirmation no. From the `Travel Reservation & E-Ticket Details' page, you will see a link for Cancel Reservation and request refund. Click this link to request refund. Your reservation will be cancelled at the same time as your E-Ticket refund is requested. Online refund can be requested for Northwest Airlines E-Tickets only (ticket number beginning with 012). All the flights in the reservation must be marketed by Northwest Airlines and KLM Royal Dutch Airlines.

Please note: Some special offers do not allow a refund. These exceptions are noted in the terms and conditions of the special offer. Please read all conditions carefully before purchasing your ticket.