I need to create a distribution list in exchange and the requirments that end users should be blocked from expanding the list so that they don't see who are the members of the list. The group will be avaliable to all users (not hidden). Thanks

Technically, you cannot hide group membership for a distribution group in Exchange 2007. (ref: http://technet.microsoft.com/en-us/library/dd577075(v=exchg.80).aspx ) However, the work around would be to create a dynamic distribution group. This would essentially serve the same purpose. Thanks, Matt