Since you say you reinstalled everything, make sure your $ORA_HOME/network/admin/tnsnames.ora and $ORA_HOME/network/admin/sqlnet.ora files are set up correctly. You'll need to talk to your DBA for the correct settings for these files.
Well I would think they are ok since the other apps are able to connect just not my Perl scripts, heres, what I remember from my Activestate Perl installation, I was able to check the 'Add Perl to the Path Environment' and 'Create Perl file extension association' but not 'Create IIS script mapping for Perl' or 'Create IIS script mapping for Perl ISAPI'. Would this have anything to do with it?