Sorry I missed you on #alug
You might be able to tweak around that in the bios...does memtest and/or the BIOS memory count confirm the full amount of RAM ? Does memtest show any errors when checking.
The 3.2GB shown by a 32bit operating system would be normal..Windows32 certainly does this due to the address space reserved by the kernel..I presume linux does the same. However AFAIK memtest even running as it does in 32bit mode should show the full amount...well at least up to 4GB I presume it has issues above that.
You can on both Windows and Linux enable PAE mode which will give you access to the full 4GB but only in 32bit pages (minus the kernel address overhead) search the relevant documentation for your OS to find out how.
Often better memory support is added to later Bios updates..are you running the latest bios image for your systemboard ?