ulandy09, welcome to the forums
probably your graphics card is using part of that memory. And 32 bits cannot address it all.
Take a look at this article
My Computer
Computer Manufacturer/Model Number
Wally, Innc.
OS
Windows 7 x64 finally!
CPU
AMD Athlon II X2 240
Motherboard
Biostar TA790GX XE
Memory
OCZ Platinum 4GB DDR2 1066 (will not work past 800MHz)
Graphics Card(s)
MSI R4670-MD1G Radeon HD 4670 1GB 128-bit GDDR3
Sound Card
ATI High Definition Audio Device Realtek ALC888
Monitor(s) Displays
HP w19e
Screen Resolution
1440x900
Hard Drives
Western Digital Caviar Green WD5000AADS 500GB SATA
Western Digital Caviar Blue WD5000AAKS 500GB SATA