Silvery - 4:27 pm on Apr 16, 2010 (gmt 0)
Depending upon what you want to do, one can create a "one-site" approach, or a "multi-site" approach.
For instance, if you wanted your content to be optimized best for Bolivia so that it would likely rank better when searched in the Bolivian version of Google (http://www.google.com.bo/) you might want to have a site that uses the Bolivian top-level domain suffix: ".BO".
Using country-specific domains is a strong signal that content is more relevant to the people in that country.
Unfortunately, that approach is going to be much more complicated if you're trying to do content for many dozens of countries.
If, due to the complexity involved in creating multiple country domains, you need to use just one site, then making each webpage "sing" to the search engines for that country/region/city becomes of highest importance. To do that you would include the city and country names in multiple places throughout the page, and you might consider adding a geotag into the page which contains coordinates for the country's centroid.