adding other subs to.img possible ?

[Little Raven]

I have an .img file of the movie Traffic but unfortunately it came with scandinavian subs only and with all the Spanish in the beginning I really need the english subs.

Is there a way to get and add the english subs to this file ?
and what would be the best way to do it ?

I can encode divx but I'm a total newbie when it comes to dvdr ...

thanks for any help.