Add a user to an active directory group

How do I use the IADsGroup.Add function to add a user to a security group in my windows domain.

I have added the user to the domain as follows:

DirectoryEntry de = new DirectoryEntry();

// Set credentials of an AD account that is priveledged to be able to create users
de.Username = username;
de.Password = password;

// Set active LDAP path
de.Path = LDAPpath;

// Assign the users in the LDAPpath to a variable so we can manipulate it (add users)
DirectoryEntries users = de.Children;

// Add user account
DirectoryEntry user = users.Add("CN=" + LastName + "\\, " + FirstName, "user");

// Set additional properties of new account
user.Properties["samAccountName"].Add(username); // Login name
user.Properties["givenName"].Add(FirstName); // First Name
user.Properties["sn"].Add(LastName); // Last Name

// Commit changes
user.CommitChanges();

ActiveDs.IADsUser tester = (ActiveDs.IADsUser)user.NativeObject;
tester.ChangePassword("", Mypassword);

// Commit password changes
user.CommitChanges();


Now how do I add this user to the security group named :

My Standard Group


Thanks!