If anybody wants to create their own FPS game I would recommend the software FPSCreator.It comes preloaded with sounds,terrains, maps to make your own game.(for more info just google it)

Since you have a old computer I wont recommend any new games like FEAR,GUN, but instead would advise you to play old FPS games like THE Mummy,Tomb Raider, and other pre-2003 releases

This is one excellent game
First off The character you play in fear can only carry 3 weapons at a time, which is more realistic as some FPS games allow you to carry a ridiculous amount of weapons
The Graphics effects in Fear are breathtaking better than anyother FPS in my opinion.
If you like FPS ...