Is it possible to differentiate Windows PE and other Windows (e.g., Windows 2003, Vista)?

Hello,

Is it possible to differentiate Windows PE and other Windows (e.g., Windows
2003, Vista)?

Background: I want my program to run on only Windows Server OS (Windows
2000/2003/2008) and WinPE, not Client OS (Windows XP/Vista). But when my
program run on WinPE, it shows that it is running on Vista. So I want to
find a way to differentiate Windows PE and other Windows. e.g., there might
be some trick in WinPE to identify it is a WinPE, not other Windows.

Thanks!