I created this report to demonstrate how you can construct a list of groups and members that includes additional details about the members.
The report is grouped on the name of the group and presents the CN, samaccountname and Department name for each member.
It was built using a custom query - the content of which was based on the built-in "Group Membersship by Domain Account" report.
The key thing about this query is this part:
LEFT OUTER JOIN [tblDomainUser] DomUserInfo
ON ([vwDomainGroupMember].[AccountID] = [DomUserInfo].[AccountID])
...where I am JOIN'ing with the tblDomainUser table in the ER DB to grab additional user attributes from these fields: CommonName (which I re-label as Fullname) and Department.
I created the layout from scratch as well. The only "trick" in the detail band of the layout is to make sure that you suppress duplicates of all the detail fields.
Feel free to ping me with questions.