The Net::SCP module depends upon you having one or another or yet another implementation of scp already installed on your system. Since each of those (and any other options that might exist) use a different convention as to where they store their key files, it will be hard to help you without knowing which tool you are using.
If you do not yet have a version of scp installed, I would recommend CygWin (since it is free and ends up looking pretty linux-y). If you do that, don't install or use their version of perl.
Alternately, you could use Net::SSH::Perl and do it purely in perl. The pscp script that comes with it should get you started ...
The intelligent reader will judge for himself. Without examining the facts fully and fairly, there is no way of knowing whether vox populi is really vox dei, or merely vox asinorum. — Cyrus H. Gordon