In addition to what others have said, you can install modules in non-standard places by using the PREFIX argument when you run Makefile.PL. For instance, from your examples it appears you might want to install your modules like this:

$ perl Makefile.PL PREFIX=/var/tmp/perl
$ make
$ make test
$ make install
[download]

You should read perldoc perlmodinstall for a more complete overview of installing modules. You may also find some useful information in tachyon's tutorial, A Guide to Installing Modules, available in the Tutorials section.

-sauoq
"My two cents aren't worth a dime.";