Just one extra tip in addition to jettero's advice: The easiest way to add another directory to your library path is to put use lib '/path/to/directory/with/modules'; at the top of your script. After you do that, you can use your own modules as if they were installed in the normal place -- you can even upload pure-perl modules from CPAN there and have them work fine.

Note that you probably don't want to just put the modules alongside your script, though -- it's a good idea to put your modules in a directory that's not web-accessible so there is no risk of visitors to your site being able to view their source code.