Today there was a curious case where someone's Windows 7 Eee PC had 2 GB of RAM, which the operating system was aware of, but only listed as 767 MB available for use.
It turns out that if the Boot Booster is enabled in the BIOS, it limits the amount of usable RAM. To fix this, press F2 during boot-up, go to the Boot menu, use the arrow keys to highlight Boot Booster and press Enter to change it to Disabled. Next press F10 to save, then reboot and you are done.
Note: You may still only have 1.75 GB usable, but that can be blamed on the leeching onboard video.