This works fine for me with Activestate Perl Build 630 using the Perl Package Manager (PPM).

C:\>ppm
PPM interactive shell (2.1.5) - type 'help' for available commands.
PPM> install Tk
Install package 'Tk?' (y/N): y
Installing package 'Tk'...

.
.

Writing D:\Perl\site\lib\auto\Tk\.packlist
PPM> query Tk
Tk [800.022] Tk - a Graphical User Interface Toolkit
PPM>
[download]

 

perl -e 's&&rob@cowsnet.com.au&&&split/[@.]/&&s&.com.&_&&&print'