How to know if DirectoryEntry is a user or a group?

Off the top of my head: Have you considered checking Schema properties of the returned result? I'm thinking you could easily figure a group by using DirectoryEntry.SchemaEntry.Name. It should return group if your schema entry is a group.

Reference: MSDN: DirectoryEntry.SchemaEntry

---

Just out of curiosity and a bit off topic in your code above:

 if (pathToAD.Length > 0)
      objADAM = new DirectoryEntry();
 else
      objADAM = new DirectoryEntry(pathToAD);
 objADAM.RefreshCache();

wouldn't you want to use pathToAD IF the Length>0?