Use the Win32::AdminMisc module available from www.roth.net.

Here's how to use ppm

PPM> set repository roth http://www.roth.net/perl/packages
PPM> install Win32-AdminMisc
[download]

As long as the program is runing as the system user, you can use this piece of code to change the user.

Win32::AdminMisc::LogonAsUser($domain,$username,$password);
[download]

I hope this helps.