Answer
The /3GB switch allows Windows XP, 2003 Server, and 2000 Server to dedicate 3GB of memory address space to a 32-bit application, instead of the usual 2GB. Machines that already have 4 or more GB of physical memory cannot make use of the /3GB switch. In this case, use of the /3BG switch will limit an application to using a maximum of 3GB and will not make use of additional memory. For more information, see the Microsoft article in the Related Information.
Warning:
ESRI has neither tested nor certified this configuration. ESRI does not support its use with ArcGIS or other ESRI products.