function GetUserName : String;
var
pcUser : PChar;
dwUSize : DWORD;
begin
dwUSize := 21;
GetMem( pcUser, dwUSize );
try
if Windows.GetUserName( pcUser, dwUSize ) then
Result := pcUser
finally
FreeMem( pcUser );
end;
end;
Ejemplo de llamada:
Label1.Caption:=GetUserName;