Disney's full-service downloads limit you to 120 pics per CD, even if more wil fit on the CD.
There are also self-service download machines in the camera shops at MK and MGM, and at the Kodak ImageWorks in the Imagination pavilion at Epcot. I don't know whether the self-service machines also limit the number of pics per CD.
Price for downloading to CD either full-serve or self-serve at WDW is $12.99 per CD.
If you have a car, one of the Walgreens stores off-site is a much better alternative. All of the Walgreens stores have 24-hour photo centers; they will download your pics to CD for only $3.99 per CD, for as many pics as the CD will hold.
The number of pics that will actually fit on a standard 700mb CD varies depending on 1) What kind of camera you have, 2) What file format you are shooting in (i.e. JPG, TIF, RAW, etc.) 3) What megapixel settings you are shooting at, and 4) What compression setting (i.e. Fine, Medium, Coarse, etc) you are shooting at.
If you want to find out how many pics a CD will hold, first you need to know how big yoru pics are. Look at a bunch of them in My Computer. Switch to Details view. One of the collumns in Details view is File size; this is usually in kb. 1024kb=1mb. Each CD holds about 700mb. Divide 700mb by the average size of your pics, and you will find out roughly how many of your pics will fit on a 700mb CD.