P7 was 32bit and most household computers of that era were 32bit. In 32bit, each running process only gets 2GB of memory allotted (there is a "high address aware" trick, but that only gets you about another 1GB). Poser itself will need a chunk of memory just to hold the scene, and the 2GB memory limit applies to the total of P7 and Firefly. So, to avoid running out of memory when rendering, you have the option to run Firefly as its own process, separate from Poser 7. That allows Firefly its own 2GB of memory, while Poser 7 gets its own allotment.

Is your Windows 7 32bit or 64bit?

Which version of Windows 7 do you have?

How much memory is in your computer?

How much memory is your computer capable of reading? (This is determined by the main chipset on the motherboard)

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5