Fixed width data is probably the most annoying data to import because you need some mechanism to break the columns at the column boundaries. A lot of people bring this kind of data
into a tool such as OpenOffice, Excel or MS Access, massage it into a delimeted format and then pull it in with PostgreSQL copy command or some other means. There is another way and one that doesn't require
anything else aside from what gets packaged with PostgreSQL. We will demonstrate this way.
Its quite simple. Pull each record in as a single column and then spit it into the columns you want with plain old SQL. We'll demonstrate this by importing Census data places fixed width file.
Although this technique we have is focused on PostgreSQL, its pretty easy to do the same steps in any other relational database.
Both David Fetter and Dimitri Fontaine have demonstrated other approaches of doing this as well
so check theirs out.