config problems

Hi,

I have some problems configuring postgresql 7.0 .  I am using the rpms
on a redhat 7.1 distribution.  I want to change the option -N to 64 and
the -B to 128.  I put this in the postmaster.opts.default file but when
I restart postgresql and I take a look at the status, it uses N=32 and
B=64.  Is there something I should know that isn't in the documentation
?  Can there be something wrong with the standard RedHat scripts to
start the server ?
Also, what is the best way to make an estimation of the highest number
of connections my system will be able to handle ?  (the server is a PIII
500MHz with 256MB RAM).

thank you,

Henk