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="">Select....');
document.write('<option value="../purchase/buynow_uk.htm">United Kingdom');
document.write('<option value="../purchase/buynow_us.htm">USA');
document.write('<option value="../purchase/buynow_eu.htm">Europe');
document.write('<option value="../purchase/buynow_row.htm">Rest of World');
document.write('</select>');
document.write('<input type=button value="Go!" onClick="javascript:formHandler()">');
document.write('</form>');