function formHandler(){
var URL = document.form.site.options[document.form.site.selectedIndex].value;
window.location.href = URL;
}

document.write('<form name="form">');
document.write('<select name="site" size=1>');
document.write('<option value="">Seleccione su País');
document.write('<option value="http://www.psicomundo.com/argentina/index.htm">Argentina');
document.write('<option value="http://www.psicomundo.com/brasil/index.htm">Brasil');
document.write('<option value="http://www.psicomundo.com/chile/index.htm">Chile');
document.write('<option value="http://www.psicomundo.com/colombia/index.htm">Colombia');
document.write('<option value="http://www.psicomundo.com/cuba/index.htm">Cuba');
document.write('<option value="http://www.psicomundo.com/mexico/index.htm">México');
document.write('</select>');
document.write('<input type=button value="Ir!" onClick="javascript:formHandler()">');
document.write('</form>');