I increased my 32-bit Ubuntu box from 2 GB to 4 GB RAM and found out that the box only recognized 3.1 to 3.2 GB RAM. I then install the server kernel to make it to read 4 GB of RAM and reboot afterwards.
sudo apt-get install linux-server linux-headers-server
However, my nVidia GeForce 8500GT display card cannot work under the previous installed Ubuntu restricted driver. I should install the official nVidia driver instead. Anyway, 3D desktop and 3D games are not my favorites.
For installing nVidia driver, please refer to :
Gefore 8500GT on Ubuntu 7.04
Updated on 2008-June-15 :
More complete solution is here.