NAT using /usr/sbin/ppp

[Andrei Tanase <tanase@mail.rdslink.ro>]

there are two computers, one running w2k, the other openbsd 3.0. w2k is
192.168.0.2, obsd is 192.168.0.1.
the ethernet link is working OK, i can telnet, ftp, ssh at will between
the two. i start ppp, manually dial to my isp,
the layers come up (PPP), i say "add default HISADDR" at the prompt,
"nat enable yes" and two things happen:
w2k can see the inet a-OK, it's impressively speedy AND i can't
ftp,ssh,telnet to the obsd machine anymore.
"delete default" at the ppp prompt enables me to connect again but the
NAT doesn't work then (obviously?).
established connections to the obsd machine are still working, but i
can't make new ones.

w2k:
C:\WINNT\system32>route print
===========================================================================

Interface List
0x1 ........................... MS TCP Loopback interface
0x3000003 ...00 10 dc 24 d8 a4 ...... NVIDIA nForce MCP Networking
Adapter Driver
===========================================================================

===========================================================================

Active Routes:
Network Destination            Netmask              Gateway
Interface      Metric
   0.0.0.0                            0.0.0.0
192.168.0.1     192.168.0.2      1
   127.0.0.0                        255.0.0.0
127.0.0.1         127.0.0.1          1
   192.168.0.0                    255.255.255.0      192.168.0.2
192.168.0.2      1
   192.168.0.2                    255.255.255.255  127.0.0.1
127.0.0.1          1
   192.168.0.255                255.255.255.255  192.168.0.2
192.168.0.2      1
   224.0.0.0                        224.0.0.0
192.168.0.2     192.168.0.2      1
   255.255.255.255            255.255.255.255  192.168.0.2
192.168.0.2      1
Default Gateway:       192.168.0.1
===========================================================================

Persistent Routes:
  Network Address          Netmask  Gateway Address  Metric
     0.0.0.0                          0.0.0.0      192.168.0.1
1

openbsd:
PPP ON coy> show route
Destination         Gateway             Flags  Netif
default                193.231.233.30 UGS    tun0
127.0.0.1           127.0.0.1           UH      lo0
192.168.0.0/24  link#1                 UC      rl0
192.168.0.2       00:10:dc:24:d8:a4   UHL    rl0
193.231.233.30 62.231.91.4       UH     tun0

kernel is a custom one but with ip forwarding and packet filter enabled.
i haven't messed with pf.conf && nat.conf. i read
the f***ing manuals but they are rather terse. the sample ppp confs are
not using nat anywhere.

help? what is going on here? what am i doing wrong? or is this how it is
supposed to work? this is my first ever *nix experience
so be gentle with me.

thank you.