in reply to Cannot connect Perl to PostgreSQL using ODBC (SQL-IM002)

Data source name not found and no default driver specified.

This means you did not create the proper DSN. You need to create the DSN using (for example) odbcad32.exe, or use a DSNless connection string. See http://connectionstrings.com for how to create the various connection strings.

Also, a Google search for the error message turns up many relevant replies.