The FIRST thing you should do is make sure that your Perl is installed in the default location. Because you may have done something funky and installed it in C:\perlhome\... You have to work to put it someplace non-standard, but that doesn't mean it didn't happen.
Run: perl -V from the command line and Perl will tell you all about itself, including where it is looking for libraries. THEN go back and reread all of the above posts on how to include paths in @INC :)