what you are doing is overriding the value
$a_diary each time....
you may try this:
// Setup Date Array. Start of week is 03082008
for ($wd = 0; $wd < 7; $wd++)
{
$col_name = date('dmY', mktime(0, 0, 0, date("m",$StartOfWeek) , date("d",$StartOfWeek)+$wd, date("Y",$StartOfWeek)));
$a_diary[$col_name] = array("00" => ".", "01" => ".", "02" => ".", "03" => ".", "04" => ".", "05" => ".", "06" => ".", "07" => ".", "08" => ".", "09" => ".", "10" => ".", "11" => ".", "12" => ".", "13" => ".", "14" => ".", "15" => ".", "16" => ".", "17" => ".", "18" => ".", "19" => ".", "20" => ".", "21" => ".", "22" => ".", "23" => ".");
echo '<br>col_name = '.$col_name;
echo '<br>$a_diary['.$col_name.']["15"] = '.$a_diary[$col_name]["15"];
}
echo '<br>Show diary array for the week';
echo '<br>$a_diary["03082008"]["15"] = '.$a_diary["03082008"]["15"];
echo '<br>$a_diary["04082008"]["15"] = '.$a_diary["04082008"]["15"];
echo '<br>$a_diary["05082008"]["15"] = '.$a_diary["05082008"]["15"];
echo '<br>$a_diary["06082008"]["15"] = '.$a_diary["06082008"]["15"];
echo '<br>$a_diary["07082008"]["15"] = '.$a_diary["07082008"]["15"];
echo '<br>$a_diary["08082008"]["15"] = '.$a_diary["08082008"]["15"];