What could be the reason for EXTREMELY slow INSERTs?

I have this little test application that compares
retreiving and inserting data using indexes and not using
indexes. I have tried this program on two different
machines. One is a PIII 533 256 meg memory and SCSI. The
other one is a dual 400 (something) 512 meg memory. The
thing is that the PII _SELECTS_ faster (this is OK since
the program uses one thread/process) than the dual 400 but
inserts is a complete different story.

10000 inserts takes 665 seconds on the PIII 533, while on
the dual 400 it takes about 13 seconds (*GULP!*). I have
done a clean reinstallation (dpkg --purge postgresql, apt-
get install postgresql) and tried it again. Same results.
Do you guys know what could be the reason?

Thanks.

Daniel Åkerud