your page file just doesn't grow, initially when you first install the OS, the default page file is created, and the size stays as it is, then depending on the usage of the system we designate the size of the page file.
what page file is and what it does is expalined very well by johncurtis.
its recommended that the min size of page file be 12MB more than the physical RAM installed in the system, the maximum can be twice or thrice of the RAM, depending on what ur system is used for and on the availabilty of space in the partition where the page file is. you can put the page file in any partition you want, but some, maybe around 10MB should be allotted in the drive where WIN NT is installed.
alloting too much for paging is not a good idea, since excessive paging can slow down the system, so if the system gets too slow then reduce the amount of poage file desinated and viceversa, hope this helps.
In Win NT you can change the page file size from, Control Panel |System|Performance tab| change button.