Sharing a folder on a different domain

I am trying to share a folder from (server 1) on (domain 1) to another computer linked to (server 2) on (domain 2). I have taken the following steps and can't get past the last one:
Explorer
Network
(server 1)

Here it won't show the files available to be shared on (server 1) until I put in a password. I have credentials to log in to that server to get access but I don't know how to type the username and password. I have tried username@domain (which worked on a windows xp) & just the username and password, but it doesn't allow me through. so my question is:

How do you type the username and password when trying to share a folder on a different domain.

Thanks in advance!