Different ram/gpu size shown

hi friends,

this is a weird observation..i dont know why. please explain.

i have 2 GB of RAM in 2 slots = 4GB total ( 3.85 to 3.9 GB)
in bios i set shared by gpu = 256MB

system properties show ram=3.25GB
GPUZ shows gpu mem=256MB

so where is the rest of the ram?
logically the system should show nearly 3750MB or near 3650MB (i know it is never round figures)

my configs are---------------

Processor
Model : AMD Phenom(tm) 8650 Triple-Core Processor
Speed : 2.3GHz Cores per Processor : 3 Unit(s)

Mainboard : Asus M3N78-EM

Chipset
Model : AMD F10h Athlon 64/Opteron/Sempron HT Hub
Front Side Bus Speed : 2x 1.8GHz (3.6GHz)
Total Memory : 4GB DIMM DDR2
Memory Bus Speed : 2x 333MHz (666MHz)

Memory Module(s)
Memory Module : Transcend JM800QLU-2G 2GB DIMM DDR2 PC2-6400U DDR2-800 (5-5-5-18 3-23-6-3)
Memory Module : Transcend JM800QLU-2G 2GB DIMM DDR2 PC2-6400U DDR2-800 (5-6-6-18 3-24-6-3)

Video System
Video Adapter : NVIDIA GeForce 8300 (24 SP 1.5GHz, 256MB DDR2, Integrated Graphics)

Graphics Processor
Adapter : NVIDIA GeForce 8300 (8SP 1C 1.5GHz, 253.7MB, Integrated Graphics)

Are you running Win XP 32-bit? I seem to recall there was an upper limit to RAM around 3.5GB.