Question about Files Operation, Microsoft'error

         I want to Design a program,it can delete the files which  exist /exceed 15-days.
I use the fileInfo's Creationtime and the local time,and compare them,if fit to the condition,I delete the file.                 
        but when we cut a file or use winzip to extract a zip file,the file' Creationtime don't change .                
         for example, if the file "aa.txt" ,its Creationtime is 2005-09-23, the local time is 2005-12-16,you cut it ,and paste it to another directory, the file's creationtime still is 2005-09-23.
so ,if you use the creationtime to design the program,it will be some bugs in you program.

        Because of the bugs from Bill,I can't use the creationtime to design my program.

        so,beg for your help.  Thank U for Ur Help first.Thank.