PostgreSQL 8.0.3 limiting max_connections to 64 ?

Hello, i need help...

i have a postgresql 8.0.3 database running on the backend of a postfix
setup ( i didn't trust Mysql for the job ) on Linux kernel 2.6.8.1,
serving email to a dozen different virtual domains ( including this one
i'm using right now )...

however, this setup takes a whole lot of simultaneous connections to the
database
( postfix, amavis-new, clamav + spamassassin, apache+squirrelmail,
courier-authlib and courier-imap ), all those services were configured
to use Unix Domain Sockets, instead of TCP ( netstat -anvp showed too
many short-lived connections were kept on CLOSE_WAIT for too long while
connecting via TCP ), and, despite i have made max_connections on the
postgresql.conf as high as 500, after ( around ) 64 simultaneous
connections i start having a lot of "sorry too many clients already"
errors on my postgresql logfile...
then, my users go nuts complaining about how slow the server is and/or
having to retype their passwords too many times ( of course, since
authlib can't pick a connection to authenticate against the database ).

max_connections, shared_buffers, shmmax were tweaked, but the server
does not seems to respect the 500 max_connections...
i *know* i'm missing something obvious, but, what could be wrong ?...
i'm lost... any help would be most appreciated... please.

thanks.