Can't increase max connections

I have installed PostgreSQL 7.3 on FreeBSD 4.10 Stable, and have been trying to increase the max connections. the most I'm able to is 40, if I increase it any higher I'm unable to start the database. Is there any tip, s hte any guide where I can get an idea of the other values to set in postgresql.conf for increasing max connections? I had also recompile the kernel and changed maxusers from 0 to 64. I'm not sure if increasing it even more would allow me increase connections. Would appreciate some help, thanks.