I would recommend using the reports module.
to set it up for showing every roll and only the user name and roll you would enter this into the sql: SELECT users.username, roles.rolename FROM users, roles WHERE users.username = roles.rolename order by rolename

to set it up for showing only users within a roll (you can name the module as the role name, note* replace Administrators with the role name) you would enter this into the sql: SELECT users.username, roles.rolename FROM users,
roles WHERE users.username = roles.rolename and rolename = 'Administrators'

you can also use the same type of sql select in the dynamic forums module and have a drop down box. I use it to send mass emails for different committees (custom user profile) and here is what my select statement looks :
SELECT 'All Users' as QuestionOption, Stuff(
(SELECT N'; ' + email FROM users where email>=' ' FOR XML PATH(''),TYPE)
.value('text()[1]','nvarchar(max)'),1,2,N'') as QuestionOptionValue
Union
SELECT 'All Volunteers' as QuestionOption, Stuff(
(SELECT N'; ' + email FROM dbo.udf_UserProfileField(' Volunteer') AS Volunteer left OUTER JOIN dbo.vw_Users AS U ON Volunteer.PortalId = U.PortalId AND Volunteer.UserID = U.UserId where propertyvalue='True' FOR XML PATH(''),TYPE)
.value('text()[1]','nvarchar(max)'),1,2,N'') as QuestionOptionValue
union
SELECT 'All Committees ' as QuestionOption, Stuff(
(SELECT N'; ' + email FROM dbo.udf_UserProfileField('Committee') AS Committee left OUTER JOIN dbo.vw_Users AS U ON Committee.PortalId = U.PortalId AND Committee.UserID = U.UserId where propertyvalue>' ' FOR XML PATH(''),TYPE)
.value('text()[1]','nvarchar(max)'),1,2,N'') as QuestionOptionValue

Ill be around all night as I am working, if you need any help send me a message and I will give you my aol im or email which ever is easier for you