NT Service in WinXP, strange behaviour

Hi, gurus.
I have a NT service program that is ruuning ok on Win2k, inside it I use MessageBox with (MB_OK | MB_ICONINFORMATION | MB_SERVICE_NOTIFICATION) flag to pop some warning message.
Another important thing is theis sevice is use interactive. so in Win2k, it can change the desktop color.
Eveything is fine until in WinXP. I never saw the message box, and the service never chage the desktop color.
At first I suspect WinXP need explicit code to access the desktop, so I use MSDN Q173687 to add access to the default desktop. but failed in vain.
Why WinXp can not show MB_SERVICE_NOTIFICATION message box? and how to change desktop setting in an interactive NT service in WinXp?
any help will be highly appreciated, and thanx ahead.