One problem many people may experience with deleting files on Win32 systems is the lock IIS4 places on recently served files (MS Knowledge Bank article Q184956).
Using ActiveState Perl or PHP4, unlink() will be unable to delete files such as html pages or images which have been served up to a minute ago. Naturally this is VERY frustrating if your site is popular, as files are being served all the time.
One solution I seem to remember was to try renaming the file, then delete it. If anybody knows a solid way of deleting files in IIS, please share it!