In your HTML file something like this
<select name="db_table">
<option value="option_1">Option 1</option>
<option value="option_2">Option 2</option>
<option value="option_3">Option 3</option>
<option value="option_4">Option 4</option>
</select>
In the form handler
$option = $_POST['db_table'];
switch ($option){
case 'option_1':
$table = 'table_1';
break;
case 'option_2':
$table = 'table_2';
break;
case 'option_3':
$table = 'table_3';
break;
case 'option_4':
$table = 'table_4';
break;
}
$sql = mysql_query('INSERT INTO '.$table.' whatever you want to insert here');
This should help you along the way.