firewall without nat

[Bryan Irvine <bryan_(_dot_)_irvine_(_at_)_kingcountyjournal_(_dot_)_com>]

Is it possible to do firewalling without NAT (he asked knowingly).

How is this done?
I'm going to be replacing an old linux firewall with an openbsd one
(preferably) but those machines need to be acessable via the outside
world (web servers mail servers, etc etc...).   

--Bryan