Oncelikle System.Directory Services referansını projemize eklemeliyiz.

C#

DirectoryEntry entry = new DirectoryEntry(LDAP://domainAdi);
DirectorySearcher searcher = new DirectorySearcher(entry);
searcher.Filter="(objectClass=user)";
StringBuilder strBuilder = new StringBuilder();
foreach (SearchResult sr in searcher.FindAll())
{
   strBuilder.Append(sr.GetDirectoryEntry().Name.ToString());
   strBuilder.Append("\r\n");
}
MessageBox.Show(strBuilder.ToString());

VB

Dim entry As DirectoryEntry = New DirectoryEntry(LDAP://domainAdi)
Dim searcher As DirectorySearcher = New DirectorySearcher(entry)
searcher.Filter = "(objectClass=computer)"
Dim strBuilder As StringBuilder = New StringBuilder()
For Each sr As SearchResult In searcher.FindAll
   strBuilder.Append(sr.GetDirectoryEntry().Name.ToString())
   strBuilder.Append(vbNewLine)
Next
MessageBox.Show(strBuilder.ToString())