getHostAddrByName

BOOL InternetCheckConnection( 
LPCTSTR lpszUrl, 
DWORD dwFlags, 
DWORD dwReserved 
);

gethostname 

function NetServerEnum(const ServerName: PWideString; level: DWORD; var Buffer:
                       pointer; PrefMaxLen: DWORD; var EntriesRead: DWORD;
                       var TotalEntries: DWORD; ServerType: DWORD; const Domain: PWideChar;
                       var ResumeHandle: DWORD): DWORD; stdcall;
external 'netapi32.dll';

function NetApiBufferFree(Buffer: pointer): DWORD; stdcall; external 'netapi32.dll';

function IsNet: boolean;
var Buffer: pointer;
    EntriesRead, ResumeHandle, TotalEntries: DWORD;
begin
   ResumeHandle:=  0 ;
   Result:= false;
   if NetServerEnum(nil,  101 , Buffer, DWORD(- 1 ),
                    EntriesRead, TotalEntries, $FFFFFFFF, nil, ResumeHandle) =  0  then
   Result:= EntriesRead >  0 ;
   NetApiBufferFree(Buffer);
end;