Wow too much of information.
Since your os is 32bit,might be this is happening.
Quote from tech forum:
32 Bit OS can not and will not recognize or utilize 4GB of RAM. The Max you will get is 3.5GB of RAM recognized and utilized on a 32 Bit system.
Registers in x86 PCs are limited to 32 bits, which means the biggest number that can be stored in that register is 2^32, or 4,294,967,296;
which means that the CPU can access up to "ADDRESS 4,294,967,296" which is the 4th GB of data.
The problem is that the CPU also access I/O devices (printer, USB, keyboard, mouse, monitor, etc.) by assigning them an address as well.
So it reserves half a GB or so of the memory addresses to talk to the I/O devices... So you have 4GB - ~0.5GB -> 3.5 GB (on Windows it is 3.2GB).
Plus this also doesnt take into consideration that Video Card Memory which is also added into the resources.
So lets calculate:
your vista can see but cannot use.
3 GB-.5 GB(by OS)=2.5 GB.
2.5 GB-1 GB(VRAM)=1.5 GB.
This is reasonable.Might be there are some other resources connected to your pc which use up your ram.