Depending on your distribution, you may be able to use the Linux kernel compiled for PAE capable machines. All you have to do is install PAE kernel package (or hugemem).
This package includes a version of the Linux kernel with support for up to 64GB of high memory. It requires a CPU with Physical Address Extensions (PAE).
The non-PAE kernel can only address up to 4GB of memory. Install the kernel-PAE package if your box has more than 4GB of memory (>=4GB).
what is your distro?