The maximum CERTIFIED seating capacity for the Boeing 747 is 660 passengers. This is defined in the FAA Type Certificate Data Sheet A20WE, pages 10 and 14.
Here is a link to the FAA TCDS:
The 660 max capacity is applicable only to the -300, -100SUD, and -400 models with certain exit door configurations.
This 660 seating capacity is a certification limit, and doesn't imply that any airline has used it. The additional details and conditions for this capacity is defined in the TCDS A20WE.
[Edited 2006-01-08 19:23:54]
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.