type
 PWKSTA_USER_INFO_1 = ^TWKSTA_USER_INFO_1;
 TWKSTA_USER_INFO_1 = record
   wkui1_username:LPWSTR;
   wkui1_logon_domain:LPWSTR;
   wkui1_oth_domains:LPWSTR;
   wkui1_logon_server:LPWSTR;
 end;

function NetWkstaUserGetInfo(reserved:PWChar; level:DWORD;
 bufptr:Pointer):DWORD;stdcall;external 'Netapi32.dll' Name 'NetWkstaUserGetInfo';
function NetApiBufferAllocate(ByteCount:DWORD;
 Buffer:Pointer):DWORD;stdcall;external 'Netapi32.dll' Name 'NetApiBufferAllocate';
function NetApiBufferFree(Buffer:Pointer):DWORD;stdcall;external 'Netapi32.dll' Name 'NetApiBufferFree';

procedure TForm1.Button1Click(Sender: TObject);
var
 WkUInfo:PWKSTA_USER_INFO_1;
begin
NetAPIBufferAllocate(1000,WkUInfo);
try
 NetWkstaUserGetInfo(nil,1,WkUInfo);
 RE1.Lines.Add(WideCharToString(WkUInfo^.wkui1_username));
finally
 NetApiBufferFree(WkUInfo);
end;

end;

WkUInfo:= nil;
if( NetWkstaUserGetInfo(nil,1,@WkUInfo) = 0 )then begin
  if(WkUInfo <> nil)then
     RE1.Lines.Add(WideCharToString(WkUInfo^.wkui1_username));
end;
if(WkUInfo <> nil)then NetApiBufferFree(WkUInfo);