nat and ipfw

[Michelle]

i have a freebsd server running 4.6.2 with 2 nic cards installed one 
for our lan (fxp0) that provides connection to the outside world via 
dsl and the other for an internal subnet (xl0).  i have both natd and 
ipfw configured and running.  when on the subnet, i can not connect to 
the outside.  i tried flushing the firewall rules and adding only:

ipfw add 100 divert natd all from any to any via fxp0
ipfw add 200 allow all from any to any

i am then able to connect from a client on the subnet to an outside ip 
address.

then i tried flushing the rules again and adding:

ipfw add 100 divert natd all from any to any via fxp0
ipfw add 200 allow all from 192.168.53.200 to any
ipfw add 300 allow all from any to 192.168.53.200

i don't understand why the above rules would stop the client on the 
subnet from making a connection to the outside.  is there another rule 
i need to add?