After adding use Win32;, your shutdown command worked for me (ActivePerl 5.6.1 on Win2k Pro SP4) with no changes. Keep in mind it doesn't work on all versions of Windows. The documentation states it only works on the following OSs:

• WinXP
• Win2003 Server
• Win2k Pro & Server
• WinNT Workstation & Server.

It will not work on:

• WinME
• Win98
• Win95

By the way, it would be nice if you asked the user if he wanted to reboot before calling this command.