Mudbox (32 bit) can take advantage of additional RAM when installed on a 32 bit Windows XP/Vista computer.
If you are running Mudbox (32 bit) with 4 GB of installed RAM on a Windows XP/Vista (32 bit) system and you are planning to work with models that are subdivided to more than 6 million polygons, set the following in your boot.ini file to enable Mudbox to take advantage of an additional 1 GB of virtual memory beyond the 2 GB system default:
/3GB /USERVA=2940