An interactive television program guide system is provided in which an interactive television program guide is implemented on user television equipment containing a memory. The system allocates the memory among different categories of program guide data used by the program guide. When new channels are added to the channel line-up, the program guide adjusts its memory allocation accordingly. When it is desired to install a new non-program-guide application on the user television equipment in addition to the program guide, memory can be reallocated to accommodate the new application.