Gustbook Order

Looks fine. The latest post should be first while the later post(s) will proceed in cronilogical "date" order.

I don't really use guestbooks much to test this, but either it is due to your format of day-month-year such as:

29day-07month-08year
01day-08month-08year

29 is a bigger number than 01 so it appears at the top.

You can try switching guestbook.php from:
ORDER BY `Date` DESC

to:
ORDER BY `Date` ASC

Desc=decending
Asc=Acending

Which will sometimes invert them or flip them.

Otherwise you might try changing the day_of_year thing for each month in your admin panel language key settings to change the display from:
29-07-08

to:
July 07, 2008

Then play with DESC and ASC from there.

Just a couple of thoughts.

Good Luck!!
gameutopia