如果你想要改变Windows的缺省打印机,你必须在Windows的WIN.INI中改变设备键。

发送一条 WM_WININICHANGE 消息：

var
strIni: array[0..MAX_PATH] of Char;
arrWindows: array[0..64] of Char;
begin
GetWindowsDirectory(strIni, SizeOf(strIni));
StrCat(strIni, '\win.ini');
with TIniFile.Create(strIni) do
try
WriteString('windows', 'device', 'HP LaserJet 4 Plus,HPPCL5MS,LPT1:');
finally
Free;
end;

StrCopy(arrWindows, 'windows');
SendMessage(HWND_BROADCAST, WM_WININICHANGE, 0, LongInt(@arrWindows));
end;

（出处：www）