The Pelles C compiler/IDE is FAR superior and up to date (and free). Highly recommended.
What you want to do, is already programmed into Windows XP, and imo, you should use that feature:
1) click start -->Control Panel -->Scheduled task -->Add scheduled task
2) When the wizard asks for the name of the program to run, enter mytimer.bat
3) Then create the mytimer.bat file, in the Windows/system32 directory (so it's in the path, and Windows can always find it).
4) open notepad and enter your shutdown command, into the bat file, and save it.
5) See if it works!