Okay this is from Delta. I emailed them a few days ago with the same question and this was there answer. It helped me. Hope it helps you
In order to have your Delta flights added to one of our partner
airline's frequent flyer account, you must do one of the following:
1.) You can provide your account number to a Delta agent when making
your reservation over-the-telephone or after you have purchased your
ticket on delta.com. The representative will add the partner frequent
flyer number to your reservation.
2.) If you check-in online, you will have the opportunity to add your
frequent flyer number on Step 2 of the Online Check-In process. As you
are checking-in, a list of names of will appear. The second box on this
screen is the Frequent Flyer box with the option to "add/enroll." When
you click on "add/enroll," another window will pop up. From there you
may just pick the SkyMiles partner you want and enter your number in
their program. Just click submit from there and you're all set.
3.) As a final option, you can give your frequent flyer number to the
ticket or gate agent before boarding your departing flight.
Whichever option you choose, it is important that your frequent flyer
number be added to the reservation prior to departure; this will ensure
that your miles are automatically submitted to our partner airline by
Delta. Otherwise, if you are unable to add the partner frequent flyer
number, it will be necessary for you to submit the boarding passes and
e>ticket to the partner airline in order to receive credit.
We appreciate your interest in Delta Air Lines.
Sincerely,
Rochelle Hayes
Online Customer Support Desk
http://www.delta.com