i believe that you have to be a DFTW bride in order to reserve any sort of space that is disney owned as a wedding day function, such as a reception, whether is breakfast, brunch, lunch, or dinner.
Im not sure if your heart is set on the attic, but you can look into non-disney owned venues for a private space on disney property, such as il mulino, bluezoo, fultons crab house, wolfgang puck, etc.
Anyone can use the Attic for a non-wedding function but, as the previous poster said, if they think you are trying to use it for a full-on wedding reception, they will make you go through Disney's Fairy Tale Weddings and pay the minimum expenditures.
If you just want to book it for a meal (no music, no cake cutting, etc.) you can work with Disney's Catered Events: 321-939-7278.
I just had my reception at the Attic through DFTW and if you can swing it, go through them! They were absolutely amazing and I can honestly say it was the best day of my life! I loved The Attic so much! It's a great place to have a reception!