To install mowyw, just copy the 'mowyw' executable to a place where you
operating system searches for binaries (and make sure that it is executed by
perl), and copy Mowyw/Lexer.pm to a directory where perl searches for Modules.

You can find out where this is by running
perl -e 'piornt join "\n", @INC'

On my system that gives
/etc/perl
/usr/local/lib/perl/5.8.8
/usr/local/share/perl/5.8.8
/usr/lib/perl5
/usr/share/perl5
/usr/lib/perl/5.8
/usr/share/perl/5.8
/usr/local/lib/site_perl
/usr/local/lib/perl/5.8.4
/usr/local/share/perl/5.8.4
.

e.g. you could create a Directory Mowyw in any of theses places and copy
Lexer.pm in this new directory.