landrush | Vagrant plugin that provides a simple DNS server | DNS library

There are basically two ways. Both are difficult for the inexperienced. (and maybe even for the experienced)

• do a stepwise migration, using a few intermediate versions (which will probably have to be compiled from source). Between versions you'd have to do a pg_dump --> pg_restore (or just the psql < dumpfile, like in the question). A possible path first hop could be 7.4 -> 8.3, but maybe an additional hop might be needed.
• Edit the (uncompressed) dumpfile: remove (or comment out) anything that the new version does not like. This will be an iterative process, and it assumes your dump fits into your editor. (and that you know what you are doing). You might need to redump, separating schema and data (options --schema-only and --data-only, I don't even know if these were available in PG-7.4)

BTW: it is advisable to use the pg_dump from the newer version(the one that you will import to). You'll need to specify the source host via the -h flag. The new (target) version knows about what the new version needs, and will try to adapt (upto a certain point, you still need to use more than one step) I will also refuse to work if it cannot produce a usable dump. (In which case you'll have to make smaller steps...)

Extra:

• if the result of your failed conversion is complete enough, and if you are only interested in the basic data, you could just stop here, and maybe polish a bit.
• NOTICE: using pg_pltemplate information instead of CREATE LANGUAGE parameters I don't know what this is. Maybe the way that additional languages, such as plpgsql, were added to the core dbms.
• ERROR: language "plpgsql" already exists : You can probably ignore this error. -->> comment out the offending lines.
• DETAIL: Views that do not select from a single table or view are not automatically updatable. This implies that the postgres RULE rewrite system is used in the old DB. It will need serious work to get it working again.