INSERT extremely slow with large data sets

Hi Everyone,

This is my first post here so please tell me to go somewhere else if this
is the wrong place to post questions like this.

I am using PostgreSQL 7.3.2 and have used earlier versions (7.1.x onwards)
and with all of them I noticed same problem with INSERTs when there is a
large data set. Just to so you guys can compare time it takes to insert
one row into a table when there are only few rows present and when there
are thousands:

Rows Present Start Time Finish Time
------------------------------------------------------------
100 1068790804.12 1068790804.12
1000 1068790807.87 1068790807.87
5000 1068790839.26 1068790839.27
10000 1068790909.24 1068790909.26
20000 1068791172.82 1068791172.85
30000 1068791664.06 1068791664.09
40000 1068792369.94 1068792370.0
50000 1068793317.53 1068793317.6
60000 1068794369.38 1068794369.47

As you can see if takes awfully lots of time for me just to have those
values inserted. Now to make a picture a bit clearer for you this table
has lots of information in there, about 25 columns. Also there are few
indexes that I created so that the process of selecting values from there
is faster which by the way works fine. Selecting anything takes under 5
seconds.

Any help would be greatly appreciated even pointing me in the right
direction where to ask this question. By the way I designed the database
this way as my application that uses PGSQL a lot during the execution so
there was a huge need for fast SELECTs. Our experiments are getting larger
and larger every day so fast inserts would be good as well.

Just to note those times above are of INSERTs only. Nothing else done that
would be included in those times. Machine was also free and that was the
only process running all the time and the machine was Intel(R) Pentium(R)
4 CPU 2.40GHz.

Regards,
Slavisa