Sample code follows...
Function IsInGroup(UserName As String, GroupName As String) As Boolean
Dim wrk As Workspace
Dim strTemp As String
On Error Resume Next
Set wrk = DBEngine(0)
strTemp = wrk.Groups(GroupName).Users(UserName).name
IsInGroup = (Err.Number = 0)
End Function
Sub ListUserGroups(UserName As String)
Dim wrk As Workspace
Dim grp As Group
Set wrk = DBEngine(0)
For Each grp In wrk.Groups
If IsInGroup(UserName, grp.name) Then Debug.Print grp.name
Next
End Sub