Remember to setup ipfw correctly.

Sample below, uses following options:
   Localip  172.19.152.65/26
   Localnet 172.16.0.0/12
   Transparant proxy enabled for all NOT localnet destinations 80
   transproxy running at port 8081


ipfw add 10000 allow tcp from any to localhost 80
ipfw add 10001 allow tcp from any to me 80
ipfw add 10010 fwd 172.19.152.65,8081 tcp from any to no 172.16.0.0/12 80