By default, Windows places the pagefile on the boot partition where the operating system is installed. To determine the size of the pagefile multiply the amount of physical RAM by 1.5 to a maximum of 4095MB. However, placing the pagefile on the bootpartition does not optimize performance because Windows has to perform disk I/O on both the system directory and the pagefile. Therefore, it is recommended that you place the pagefile on a different partition and different physical hard disk drive so that Windows can handle multiple I/O requests more quickly.

This KB can be found @
http://support.microsoft.com/default.aspx?scid=KB;en-us;q197379