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="">All product ads:');
document.write('<option value="0810.ASP">October 2008');
document.write('<option value="0809.ASP">September 2008');
document.write('<option value="0808.ASP">August 2008');
document.write('<option value="0807.ASP">July 2008');
document.write('<option value="0806.ASP">June 2008');
document.write('<option value="0805.ASP">May 2008');
document.write('<option value="0804.ASP">April 2008');
document.write('<option value="0803.ASP">March 2008');
document.write('<option value="0802.ASP">February 2008');
document.write('<option value="0801.ASP">January 2008');
document.write('<option value="0712.ASP">December 2007');
document.write('<option value="0711.ASP">November 2007');
document.write('<option value="0710.ASP">October 2007');
document.write('<option value="0709.ASP">September 2007');
document.write('<option value="0708.ASP">August 2007');
document.write('<option value="0707.ASP">July 2007');
document.write('<option value="0706.ASP">June 2007');
document.write('<option value="0705.ASP">May 2007');
document.write('</select>');
document.write('<input type=button value="Submit" onClick="javascript:formHandler()">');
document.write('</form>');