Exactly what Tera said. You should have received a confirmation e-mail from DU with their reservation number.
To confirm your status you go to DU's website at
www.dreamsunlimitedtravel.com and select the Client Services button that appears near the top, middle of the page. There you'll just need to enter your DU reservation number and the password you provided them when booking. Then, you should be able to review yoru reservation.
From my expereiences with DU, you will not receive any paper mailing from them regarding a
DCL cruise reservation. What you will receive are e-mails from them confirming your reservation and payment. You can always check your reservation status through their website.
The only physical thing you'll receive is the DCL documents that, in our DCL cruise bookings through DU, have always come directly from DCL. You'll get this anywhere from 30 days to about a week from your cruise date.