This information is stored in tblUsersInGroup.
Basic report for a user overview:
Select tblComputers.Computername, tblComputers.ComputerUnique,
tblComputers.Domain, tblUsersInGroup.Groupname, tblUsersInGroup.Username,
tblUsersInGroup.Admingroup
From tblComputers Inner Join
tblUsersInGroup On tblComputers.Computername = tblUsersInGroup.Computername
Order By tblComputers.Computername, tblUsersInGroup.Groupname