You need to make sure the MD5 perl module is installed, for starters. You can check the contents of @INC via:
> perl -e 'print join(":",@INC)'
for a nice, PATH-ish look
Basically, @INC includes the list of directories perl will search to find your module. If you are sure the module is installed, but perhaps not in this path, just add the new directory to the @INC array.