The system memory that is reported in the System Information dialog box in vista

The system memory that is reported in the System Information dialog box in Windows Vista is less than 4GB if 4 GB of RAM is installed. Does anyone have the same problem, i.e. 4gb installed only 3gb or 3.5gb showing in Vista, apparently you have to remap memory to get it to detect the 4gb. There is a function in BIOS that allows this, here is the link that microsoft has on their website in regards to this problem. Does anyone know if my motherboard has the memory remap feature( as there is no general name for this feature) specs for BIOS,

Phoenix - Award WorkstationBIOS,  BIOS Version 6.00 PG, SMBIOS 2.3, BIOS ID; MCP61M-AM-6A61KE11C-00, ACER R01-B1, Motherboard-EM61SM/EM61PM, Chipset AMD 1100, this BIOS is exclusive to ACER, my computer is an OEM.  

Anyhelp would be greatly appreciated

regards

Gerard