SharePoint, .Net, SQL, MS BI, Collaboration and Gadgets

Here are some simple codes to do it:

1. Add the group (newMembersGroup)
2. Set the permissions of the group (role assignment) to contributor
3. Add the author to the group.
4. Associate the group to the site.
Dim groupOwner As SPUser = site.Author
site.SiteGroups.Add(newMembersGroup, groupOwner, Nothing, “”)

Dim membersGroup As SPGroup = site.SiteGroups(newMembersGroup)
membersGroup.OnlyAllowMembersViewMembership = False
membersGroup.AllowMembersEditMembership = False
membersGroup.AllowRequestToJoinLeave = True
membersGroup.AutoAcceptRequestToJoinLeave = True
membersGroup.Update()

Dim contributor As SPRoleDefinition = site.RoleDefinitions.GetByType(SPRoleType.Contributor)
Dim membersRoleAssignment As SPRoleAssignment = New SPRoleAssignment(CType(membersGroup, SPPrincipal))
membersRoleAssignment.RoleDefinitionBindings.Add(contributor)
site.RoleAssignments.Add(membersRoleAssignment)
‘Add the site author as a member
membersGroup.AddUser(site.Author)
membersGroup.Update()
site.AssociatedMemberGroup = membersGroup
site.Update()
More info in Role Assignments: http://msdn2.microsoft.com/en-us/library/microsoft.sharepoint.sproleassignment.aspx

More info to create your Group (now Cross Site Groups) : http://msdn2.microsoft.com/en-us/library/microsoft.sharepoint.spgroupcollection_methods.aspx