freebsd 5.2 and max_connections

Hello -
I am using postgresql to hold aliases, users, and relay_domains for postfix and courier to do lookups from.  I am not
storingmail in sql. 

I need postgresql to have fast read performance, so i setup index's on the tables.  Also, the queries are basically
"selectblah from table where domain='domain.com'";, so i dont need to be able to support large results. 

I will  have a lot of mail servers connecting to this postgresql db, so i need to support a lot of connections... but
dontneed to support large results. 

I am using FreeBSD 5.2.

What are some tuning options and formulas I can use to get good values?

Thanks!
David