Hi Emms!!! glad you plucked up the courage to ask here, as i can't think how to help you on this one, just before reading javil's post i was thinking of virtualdub too!! it's a great freebie movie editor, so i would definately go with trying to open your .avi in that,
 
have you tried asking at the e-on website yet?

B**ger you never mentioned it had been going for three weeks!!!! seriously if you get it back or have to start again, make sure you stop the render and then save each day (making sure that the "resume render" option has been checked) then resume render. but really you should go with the render farm option on this!!! (they even have cows (Pull the "udder" one, sorry couldn't resist))

hope you get the advise you need here emma!!! good luck!!