Slowdown problem when writing 1.7million records

I am very new to PostgreSQL and have installed v7.03 on a Red Hat Linux
Server (v6.2), I am accessing the files using JDBC from a Windows 2000 PC.

I have created a small file as follows:
CREATE TABLE expafh (
postcode CHAR(8) NOT NULL,
postcode_record_no INT,
street_name CHAR(30),
town CHAR(31),
PRIMARY KEY(postcode) )

I am now writing 1.7million records to this file.

The first 100,000 records took 15mins.
The next 100,000 records took 30mins
The last 100,000 records took 4hours.

In total, it took 43 hours to write 1.7million records.

Is this sort of degradation normal using a PostgreSQL database?

I have never experienced this sort of degradation with any other database
and I have done exactly the same test (using the same hardware) on the
following databases:
    DB2 v7 in total took 10hours 6mins
    Oracle 8i in total took 3hours 20mins
    Interbase v6 in total took 1hr 41min
    MySQL v3.23 in total took 54mins


Any Help or advise would be appreciated.

Thanks
Stephen Livesey