There are random number generator Seed and Random Generator Type environment settings that should help with this problem of getting repeated point locations. In ArcGIS 10.0, go to the Geoprocessing menu, Environments..., Random Numbers, to use those environment controls. The Create Random Points (management) help page that is linked to above has a section at the very bottom about which geoprocessing environments the tool uses. Follow the link about the Random Number generator environment to see more information.