Buffer Cache question....

I am using PG 7.2 with fsync truned on but still need a more immediate
write thru.
Does PG uses the fsync (or open_sync, etc) just for the WAL or for
tables as well ?

I understand the consequence of limiting buffer cache but my application
cares more about
integrity than performance. I'd like to be able to write the data to the
physical storage ASAP,
or ideally 100% in sync mode.

I have found that by reducing the checkpoint parameters I can write the
data to disk sooner.
For example

checkpoint_segments = 1
checkpoint_timeout = 30

What else do I have to work with....?

Thanks