For most of the hotel restaurants (e.g., The Kitchen, Mama Della's, Delfino) you can call (407) 503-DINE to make reservations.
For Tchoup Chop @ the RPR, you can call (407) 503-CHOP, or go here and make your ressies online:
http://www.emerils.com/restaurants/on-line_reservations.htm
The link is also good to make ressies at Emeril's in City Walk.
Mythos in IOA: (407) 224-4534.
Some City Walk restaurants take ressies; some Priority Seating requests. Try (407) 224-FOOD for most of the City Walk restaurants. Margaritaville has its own number: (407) 224-2155. NBA City does as well: (407) 363-5919, but when I called NBA City, their message said they don't take PS requests. You can also make PS requests for the Hard Rock Cafe online:
http://www.hardrock.com/px/px/
Of course, you can also show your room key if you are staying on-site to help move you toward the front of the line.
Not sure how far ahead you can book (30-60 days?), but Emeril's and Tchoup Chop can take ressies months in advance.
Have fun!