My understanding is that a 32 bit program can use up to 2GB of memory whether it is run from a 32 bit OS or a 64 bit one. That is why some of us are so interested in the 64 bit versions of Vegas.
A 32-bit application is able to address more than 2GB on both 32-bit and 64-bit systems. On a 32-bit OS, the application must be enabled as 'large address aware' and the system that it's running on must enable the /3GB switch. If both are true, the 32-bit will be able to address as much as 3GB.
On a 64-bit OS, a 32-bit application enabled as 'large address aware' is able to address upto 4GB.
CFF Explorer allows you to change the LARGE_ADDRESS_AWARE flag on an exe file, but if the program isn't written to use larger amounts of RAM, changing the flag, by itself, does nothing.