well, that calendar is a LauncherPro calendar I am almost positive. so, it might be from a themed LP skin would be my guess.. so you might go to the LP forum and look at the theming area
but that guess assumes that it is related to the themed item below it, so I could be totally wrong
but it is a theme of some sorts looking at the notification bar & dock area and so that weather widget might be part of it
BTW, maybe if we could see the thread/post/web site it came from, we could deduce it