LDC - Load Distributed Checkpoints with PG8.3b2 on Solaris

Hello,

I am running tests with PG8.3b2 on Solaris 10 8/07 and I still see IO 
flood when checkpoint happens.
I have tried increasing the bg_lru_multiplier from 2 to 5 from default 
but I dont see any more writes by bgwriter happening than my previous 
test which used the default.

Then I tried increasing checkpoint_completion_target=0.9 but still no 
spread of IO (checkpoint_timeout is set to default 5m)

What am I missing?

How does PostgreSQL determine the Load distribution?

Regards,
Jignesh