I would have thought 3GB would have been enough. What spec is your graphics card, perhaps it is robbing some ram from the PC?
do this help
Adobe Photoshop Version: 12.0.2 (12.0.2x20101122 [20101122.r.1204 2010/11/22:02:00:00 cutoff; r branch]) x32
Operating System: Windows 7 32-bit
Version: 6.1
System architecture: Intel CPU Family:6, Model:5, Stepping:2 with MMX, SSE Integer, SSE FP, SSE2, SSE3, SSE4.1, SSE4.2
Physical processor count: 4
Processor speed: 2926 MHz
Built-in memory: 3063 MB
Free memory: 932 MB
Memory available to Photoshop: 1632 MB
Memory used by Photoshop: 78 %
Image tile size: 128K
Image cache levels: 2
OpenGL Drawing: Enabled.
OpenGL Drawing Mode: Basic
OpenGL Allow Normal Mode: True.
OpenGL Allow Advanced Mode: False.
OpenGL Crash File: Not Detected.
OpenGL Allow Old GPUs: Not Detected.
Video Card Vendor: NVIDIA Corporation
Video Card Renderer: GeForce G210/PCI/SSE2
Display: 1
Display Bounds:= top: 0, left: 0, bottom: 1080, right: 1920
Video Card Number: 1
Video Card: NVIDIA GeForce G210
Driver Version: 8.17.11.9562
Driver Date: 20091120000000.000000-000
Video Card Driver: nvd3dum.dll,nvwgf2um.dll,nvwgf2um.dll
Video Mode: 1920 x 1080 x 4294967296 colors
Video Card Caption: NVIDIA GeForce G210
Video Card Memory: 512 MB
Serial number: 92628135130726756182
Application folder: C:\Program Files\Adobe\Adobe Photoshop CS5\
Temporary file path: C:\Users\Chaz\AppData\Local\Temp\
Photoshop scratch has async I/O enabled
Scratch volume(s):
J:\, 931.3G, 391.5G free
C:\, 910.4G, 769.3G free
Primary Plug-ins folder: C:\Program Files\Adobe\Adobe Photoshop CS5\Plug-ins\