ecco ho risolto in un altro modo per il problema precedente.

Posto il codice completo, soltanto che nn funziona solo per le province della regione Lombardia, le associa a tutta Italia.

Questo è solo un esempio, naturalmente nn sono responsabile per gli abbinamenti sbagliati prov->regione



codice:
<form>
<select name="modprovincia" onchange="this.form.modregione.selectedIndex=parseInt(this.options[this.selectedIndex].value);">
<option value="00-XX">Tutte le provincie</option>
<option value="15-AG">Agrigento</option>
<option value="12-AL">Alessandria </option>
<option value="10-AN">Ancona </option>
<option value="19-AO">Aosta </option>
<option value="16-AR">Arezzo </option>
<option value="10-AP">Ascoli Piceno </option>
<option value="12-AT">Asti </option>
<option value="04-AV">Avellino </option>
<option value="13-BA">Bari </option>
<option value="20-BL">Belluno </option>
<option value="04-BN">Benevento </option>
<option value="09-BG">Bergamo </option>
<option value="12-BI">Biella </option>
<option value="05-BO">Bologna </option>
<option value="17-BZ">Bolzano </option>
<option value="09-BS">Brescia </option>
<option value="13-BR">Brindisi </option>
<option value="14-CA">Cagliari </option>
<option value="15-CL">Caltanissetta </option>
<option value="11-CB">Campobasso </option>
<option value="04-CE">Caserta </option>
<option value="15-CT">Catania </option>
<option value="03-CZ">Catanzaro </option>
<option value="01-CH">Chieti </option>
<option value="09-CO">Como </option>
<option value="03-CS">Cosenza </option>
<option value="09-CR">Cremona </option>
<option value="03-KR">Crotone </option>
<option value="12-CN">Cuneo </option>
<option value="15-EN">Enna </option>
<option value="05-FE">Ferrara </option>
<option value="16-FI">Firenze </option>
<option value="13-FG">Foggia </option>
<option value="05-FO">Forlì </option>
<option value="07-FR">Frosinone </option>
<option value="08-GE">Genova </option>
<option value="06-GO">Gorizia </option>
<option value="16-GR">Grosseto </option>
<option value="08-IM">Imperia </option>
<option value="11-IS">Isernia </option>
<option value="01-AQ">L'Aquila </option>
<option value="08-SP">La Spezia </option>
<option value="07-LT">Latina </option>
<option value="13-LE">Lecce </option>
<option value="09-LC">Lecco </option>
<option value="16-LI">Livorno </option>
<option value="09-LO">Lodi </option>
<option value="16-LU">Lucca </option>
<option value="10-MC">Macerata </option>
<option value="09-MN">Mantova </option>
<option value="16-MS">Massa-Carrara </option>
<option value="02-MT">Matera </option>
<option value="15-ME">Messina </option>
<option value="09-MI">Milano </option>
<option value="05-MO">Modena </option>
<option value="04-NA">Napoli </option>
<option value="12-NO">Novara </option>
<option value="14-NU">Nuoro </option>
<option value="14-OR">Oristano </option>
<option value="20-PD">Padova </option>
<option value="15-PA">Palermo </option>
<option value="05-PR">Parma </option>
<option value="09-PV">Pavia </option>
<option value="18-PG">Perugia </option>
<option value="10-PS">Pesaro e Urbino </option>
<option value="01-PE">Pescara </option>
<option value="05-PC">Piacenza </option>
<option value="16-PI">Pisa </option>
<option value="16-PT">Pistoia </option>
<option value="06-PN">Pordenone </option>
<option value="02-PZ">Potenza </option>
<option value="16-PO">Prato </option>
<option value="15-RG">Ragusa </option>
<option value="05-RA">Ravenna </option>
<option value="03-RC">Reggio Calabria </option>
<option value="05-RE">Reggio Emilia </option>
<option value="07-RI">Rieti </option>
<option value="05-RN">Rimini </option>
<option value="07-RM">Roma </option>
<option value="20-RO">Rovigo </option>
<option value="04-SA">Salerno </option>
<option value="14-SS">Sassari </option>
<option value="08-SV">Savona </option>
<option value="16-SI">Siena </option>
<option value="15-SR">Siracusa </option>
<option value="09-SO">Sondrio </option>
<option value="13-TA">Taranto </option>
<option value="01-TE">Teramo </option>
<option value="18-TR">Terni </option>
<option value="12-TO">Torino </option>
<option value="15-TP">Trapani </option>
<option value="17-TN">Trento </option>
<option value="20-TV">Treviso </option>
<option value="06-TS">Trieste </option>
<option value="06-UD">Udine </option>
<option value="09-VA">Varese </option>
<option value="20-VE">Venezia </option>
<option value="12-VB">Verbania </option>
<option value="12-VC">Vercelli </option>
<option value="20-VR">Verona </option>
<option value="03-VV">Vibo Valentia </option>
<option value="20-VI">Vicenza </option>
<option value="07-VT">Viterbo </option>
</select> 




<select name="modregione">
<option value="00">Tutta Italia</option>
<option value="01">Abruzzo</option>
<option value="02">Basilicata</option>
<option value="03">Calabria</option>
<option value="04">Campania</option>
<option value="05">Emilia Romagna</option>
<option value="06">Friuli Venezia Giulia</option>
<option value="07">Lazio</option>
<option value="08">Liguria</option>
<option value="09">Lombardia</option>
<option value="10">Marche</option>
<option value="11">Molise</option>
<option value="12">Piemonte</option>
<option value="13">Puglia</option>
<option value="14">Sardegna</option>
<option value="15">Sicilia</option>
<option value="16">Toscana</option>
<option value="18">Umbria</option>
<option value="17">Trentino Alto Adige</option>
<option value="19">Valle Aosta</option>
<option value="20">Veneto</option>
</select>
</form>