295GTX and Available Memory (2.5GB being seen)

I just built a new rig and yesterday just installed the 295 GTX. First, here's the Relevant Specs:

CPU: Q9650
Memory: 2 x 2GB Cosair 1066Mhz Domintor
Motherboard: EVGA 780i
Graphics Card: BFG Tech GTX 295
OS: Windows XP SP3 (32 bit)

I have some questions on how windows is seeing the memory. I know a 32 bit system is limited to seeing 3GB.

I've also read on certain forums that the memory also incluses the Graphics Card's Memory. But I would like to confirm exactly how this works.

I have 3 questions:

1. The 295 GTX is Suppose to have 1792MB of memory but only 896 is showing up in dxdiag. I know this is suppose to be mirrored, so is this how the output is suppose to be showing up? and how would I check if I for the other "mirrored" memory.

2. I previously had a 8800GTX installed with 768MB of memory. My system memory showed up as 2.75GB with this card installed.

Now with the 295 GTX, my system memory is showing up as 2.5GB installed. There is only a difference of 105MB if you count the 295 as having only 896MB, so how did I lose 250MB?

3. How does the "mirrored" memory get allocated by the OS. Should I be subtrcting 1792 from 768=1024 or 1GB difference, but then shouldn't I lose more than 250MB?

Needless to say, I'd like to know how the math works with the system memory and video memory. Any info is appreciated.