.NET LDAP Search

DotNetLDapSearch

DirectoryEntry rootEntry = new DirectoryEntry("LDAP://some.ldap.server.com");
rootEntry.AuthenticationType = AuthenticationTypes.None; //Or whatever it need be
DirectorySearcher searcher = new DirectorySearcher(rootEntry);
searcher.Filter = "(&(objectClass=user)(objectCategory=person)(SAMAccountName=some_user_name)";
foreach(SearchResult result in searcher.FindAll()) 
{
    Console.WriteLine("account name: {0}", result.Properties["samaccountname"].Count > 0 ? result.Properties["samaccountname"][0] : string.Empty);
    Console.WriteLine("common name: {0}", result.Properties["cn"].Count > 0 ? result.Properties["cn"][0] : string.Empty);
}