Exchange Admin:
Properties of pub folder, Permissions Tab, "Windows NT accounts with permissions" - add the desired user and give him/her/group "user" role.
(If you don't see this, in exchange admin, go to TOOLS|OPTIONS|Permissions and click the check marks on the bottom of the screen, numbers 1 & 2 of the 4 options.)
After you have perms as desc. above, when you're creating a new mail, u need to go to VIEW|FromField and in that field on the email, browse to or type the name of the public folder (public foler will need to be visible on the GAL, in admin under properties of pub folder under Advanced tab).
This will send the mail message from the public folder name/address.
good luck
aliciaJ