reencoded xvid ac3

hey guys, sorry if this seems like a stupid question, but i'm new to all of this. Firstly i got sweeney todd movie, but it is a "reencoded xvid ac3.avi" and i can't play it in anything i have on my macbook, even with newest xvid and dvix codecs, plz help, all i wanna do is watch it, not put on dvd or anything complicated. Please can you recommend a program or player i can use.

Thanks

 

No need to double post.. maybe this is the solution.. work through systematically.

http://forums.afterdawn.com/thread_view.cfm/618629#3737512