Trouble with phpbb installation

Hi.

Yesterday I've migrated a PHPBB mysql database on a fresh install of
postgresql 8.1.3 on a debian gnu/linux sarge 3.1.

The python script that migrate schema and data worked fine and I got
all data on the my postgresql database.

But, when the number of phpbb connected users increase (about 70-80),
postgresql go crazy.

The number of postgres process increase too and not decrease when the
php pages released the connection (I use not persistent connection on
my php cofiguration).

Changing the database parameter like checkpoint_timeout, write_mode
and shared_buffer has no effect on this strange situation.

I've noticed also that when the connected user increase after 70 the
data are not commited immediately.

After a shutdown and restart of the postgresql instance I found into
the tables the data inserted several minutes later.

It seems like the commit has a huge delay to have effect on the DBMS.

Please help me.

Federico