I don't know the details, but on a VAX one simply set up a .forward file in ones "home" (-ish) e-mail directory, and e-mail sent to that machine would be resent to the address given in the file. I would think that similar functionality should be available on whatever system you're using (without having to do much messing with sendmail.cf or the like).
Don't ask me how though.
HTH.
Cheers,
Scott.