iptables -> DNAT & SNAT

hello

i want to redirect everything going to the internet to be redirected
transparently to squid sitting on 10.0.0.10:3128. 10.0.210.200 is my
firewall. both are in the same subnet (255.255.0.0). Now i have setup the
following rules:

Chain PREROUTING (policy ACCEPT 143 packets, 27617 bytes)
pkts bytes target prot opt in out source destination
17 1020 DNAT tcp -- * * 0.0.0.0/0 !127.0.0.1 tcp dpt:80 to:10.0.0.10:3128
0 0 DNAT udp -- * * 0.0.0.0/0 !127.0.0.1 udp dpt:80 to:10.0.0.10:3128

Chain POSTROUTING (policy ACCEPT 2 packets, 138 bytes)
pkts bytes target prot opt in out source destination
0 0 SNAT tcp -- * * 0.0.0.0/0 10.0.0.10 tcp dpt:3128 to:10.0.210.200
0 0 SNAT udp -- * * 0.0.0.0/0 10.0.0.10 udp dpt:3128 to:10.0.210.200

Chain OUTPUT (policy ACCEPT 2 packets, 138 bytes)
pkts bytes target prot opt in out source destination


i know that i have will have problems with routing the proxy back through
the firewall, but i will ignore that for now. what makes me a real
headache is that in the POSTROUTING chain no rule matches the packets to
SNAT the addresses. does anyone have any clue/tip/hint/idea !?

thanks in advance !