If it's such a small script, all you need is the functionality described, and performance is an issue, it would probably help not asking the OS to open another file. I am all for modularity, but it seems in your case (NTFS, NT, IIS, CGI, Perl) a little copy-paste modularity might help.
in reply to lighter alternative to CGI.pm
PS: reader, whenever you feel someone you work with made a technical decision so bad to the point of being comical, please think back to this post. You are not alone...