The Medieval 2: Total War demo only supports CPU's with SSE2. You must of course also have a decent video card and at least 512MB RAM.
NOTE- The full game will support SSE only processors. Look here (
http://www.twcenter.net/forums/showthread.php?t=64818) for more information.
------
For detailed information on your system as a whole follow these steps-
In the botom left hand corner of your desktop click Start > Run > In the Run box type "dxdiag" (without quotes). Inside you'll find a basic summary of your system.
Take note of the amount of RAM(memory) you have, your processor and its speed, as well as your video card information, which can be found in the "Display" tab.
------
For detailed CPU(processor) information you can download this program.
http://www.cpuid.com/cpuz.php
For a complete overview of everything connected or inside your PC download this program-
http://www.cpuid.com/pcwizard.php
A very effective tool for gathering very precise system info.