Your question leads me to believe you think the gpu ram and System random access memory have to be added together; they do not.They are seperate systems, and the worst case scenario is that widows 32 bit is limited to 3.2 gig ram and 3.2 gig Vram.
I have never heard of a situation where Vram has been limited by 32 bit, but its of no matter.
Buy the graphics card you need, the one you have has a rubbish engine.
And to K1114. please post some evidence on this forum to prove you can actually get more than 3.2 gig of ram being used by any windows 32bit system. Windows reporting tools are generic cross 32/64 bit and do not take into account o/s limitation. They just tell you the physical attributes of the system.