Código PHP:
<TD height=28 colSpan=3 class="linea">
<SELECT name=f_nac_dia size=1 class="Zona_txt" id=f_nac_dia>
<option value=01 selected>1</option>
<option value=02>2</option>
<option value=03>3</option>
<option value=04>4</option>
<option value=05>5</option>
<option value=06>6</option>
<option value=07>7</option>
<option value=08>8</option>
<option value=09>9</option>
<OPTION value=10>10</OPTION>
<OPTION value=11>11</OPTION>
<OPTION value=12>12</OPTION>
.....
<OPTION value=30>30</OPTION>
<OPTION value=31>31</OPTION>
</SELECT>
<SELECT name=f_nac_mes size=1 class="Zona_txt" id=f_nac_mes>
<option value=01 selected>1</option>
<option value=02>2</option>
<option value=03>3</option>
<option value=04>4</option>
<option value=05>5</option>
<option value=06>6</option>
<option value=07>7</option>
<option value=08>8</option>
<option value=09>9</option>
....
</SELECT>
<SELECT name=f_nac_ano size=1 class="Zona_txt" id=f_nac_ano>
<OPTION value=1900 selected>1900</OPTION>
<OPTION value=1901>1901</OPTION>
<OPTION value=1902>1902</OPTION>
<OPTION value=1903>1903</OPTION>
....
<OPTION value=2003>2003</OPTION>
<OPTION value=2004>2004</OPTION>
<OPTION value=2005>2005</OPTION>
<OPTION value=2006>2006</OPTION>
</SELECT>
</TD>