This is a limitation of running a Windows 32bit operating system on your W500.
You can read all the details about this at Geoff Chappell's website: http://www.geoffchappell.com/viewer.htm?doc=notes/windows/license/memory.htm and follow the links to obtain a utility to see how your machine's memory is mapped. My W500 (4061-2HU) has the following memory configuration:
C:\Program Files\fwmemmap_x86>.\fwmemmap.exe
Map of firmware memory ranges (from int 15h function E820h)
Address Size Type
=================== =================== =================
0x00000000`00000000 0x00000000`0009EC00 1 (memory)
0x00000000`0009EC00 0x00000000`00001400 2 (reserved)
0x00000000`000DC000 0x00000000`00024000 2 (reserved)
0x00000000`00100000 0x00000000`9D3A1000 1 (memory)
0x00000000`9D4A1000 0x00000000`00006000 2 (reserved)
0x00000000`9D4A7000 0x00000000`00110000 1 (memory)
0x00000000`9D5B7000 0x00000000`00058000 2 (reserved)
0x00000000`9D60F000 0x00000000`000B7000 1 (memory)
0x00000000`9D6C6000 0x00000000`0000B000 4 (ACPI NVS)
0x00000000`9D6D1000 0x00000000`00003000 3 (ACPI Reclaim)
0x00000000`9D6D4000 0x00000000`00004000 2 (reserved)
0x00000000`9D6D8000 0x00000000`00004000 4 (ACPI NVS)
0x00000000`9D6DC000 0x00000000`00003000 2 (reserved)
0x00000000`9D6DF000 0x00000000`00027000 4 (ACPI NVS)
0x00000000`9D706000 0x00000000`00002000 3 (ACPI Reclaim)
0x00000000`9D708000 0x00000000`00207000 2 (reserved)
0x00000000`9D90F000 0x00000000`00090000 4 (ACPI NVS)
0x00000000`9D99F000 0x00000000`00060000 3 (ACPI Reclaim)
0x00000000`9D9FF000 0x00000000`00001000 1 (memory)
0x00000000`9DC00000 0x00000000`02400000 2 (reserved)
0x00000000`E0000000 0x00000000`10000000 2 (reserved)
0x00000000`FEC00000 0x00000000`00010000 2 (reserved)
0x00000000`FED00000 0x00000000`00000400 2 (reserved)
0x00000000`FED10000 0x00000000`00004000 2 (reserved)
0x00000000`FED18000 0x00000000`00001000 2 (reserved)
0x00000000`FED19000 0x00000000`00001000 2 (reserved)
0x00000000`FED1C000 0x00000000`00004000 2 (reserved)
0x00000000`FED20000 0x00000000`00070000 2 (reserved)
0x00000000`FEE00000 0x00000000`00001000 2 (reserved)
0x00000000`FF800000 0x00000000`00800000 2 (reserved)
0x00000001`00000000 0x00000000`5C000000 1 (memory) (1.5GB memory mapped at 4GB)
Summary (in MB, ignoring partial MB):
Total memory: 3990
Memory above 4GB: 1472
And the performance tab in the Vista task manager displays:
Physical Memory (MB)
Total 2517
There's nothing you can do about this, except move to the 64bit version of Vista or Windows 7. Chappell sums it up at the link above:
That 32-bit editions of Windows Vista are limited to 4GB is not because of any technical constraint on 32-bit operating systems. The 32-bit editions of Windows Vista all contain code for using physical memory above 4GB. Microsoft just doesn’t license you to use that code.
[...]
Both 32-bit and 64-bit Windows can use all of physical memory, including above 4GB, but a 32-bit Windows application has at most 3GB of linear address space through which to access any physical memory.
[...]
If you have physical memory above 4GB and wonder how it can be that the PAE kernel does not use that memory, the answer is licensing. The 32-bit code for using memory beyond 4GB is present in Windows Vista as Microsoft supplies it, but Microsoft prepares license values in the registry so that this code never gets to work with any physical addresses above 4GB.