Forwarding to a an outside email address

we have exchange 2000 and we wanted to forward certain user’s emails (who have their own mailboxes) to an outside email address. we were able to do this easily on exchange 5.5 by creating a custom
recipients and forward emails to this custom recipient. In Exchange 2000 We were able
to create the custom contact and forwarded the emails to it but when we try to send an attachement to this contact the recipeint is getting a winmail.dat atachemnent instead of the file we send. any idea why thishappens? and how to solve this issue?
thanks in advance