I have a Giada n50 htpc that i installed extra ram (exchanged - one slot)
Windows says 4gb (1.99 usuable).
ref: Mini PC Giada N50 - http://www.giadatech.com/index.php?app=product&act=show&id=45
2G DDR3-800 (1 x SO-DIMM slot, Max. 4G)
First, since there's only (1) slot the memory is working. Next, on a 32-bit OS the maximum usable is going to be 3.0GB~3.5GB. So I would boot into the BIOS and look and see how much RAM is being shared to the GPU in addition to the spec: (512MB VRAM on board).
I looked at the manual an it's useless. The best assumption is a 'shared' amount of RAM somewhere listed in the BIOS.