I saw Donnie Darko last night.
And as soon as I got out I wanted to know what possible explanation there could be for the story and (most importantly) for the ending. It took me a long time to come up with any satisfactory explanation so for the benefit of others here are the sites that really helped:
28:6:42:12 an MSN group that has (amongst other things) the complete text of ‘The Philosophy of Time Travel’
The best explanation I could find (I’m not entirely happy with it but as the film was clearly left ‘open’ it may be the best I’m going to get it)
Its also clear to me from reading the comments of others that the director’s commentary track on the DVD goes a long way towards giving a full explanation (but doesn’t quite give you everything). I plan to get hold of the DVD and will post another story if my findings are interesting enough