check out http://mapserver.gis.umn.edu/ an opensource mapping program for which I have a particular fondness. The program has a Perl/MapScript module that allows you to construct a fully capable, web mapping site. You will need geographic data for the world map background, and a table of countries with their x,y.

Now, that is the most full-fledged solution. Whether or not you decide to use MapServer, you will need a table of countries with their x,y, and a base worldmap graphic. You could always use Imagemagick or GD to overlay a point graphic on top of the basemap graphic.