To perform transparent proxying, the computer in question MUST be in the routing chain between the source and the destination.
And yes, 0.0.0.0/0 is "anywhere." As a sample rule, on my box, iptables -L reveals:
Code:
ACCEPT tcp -- anywhere anywhere tcp dpt:ssh
while iptables -L -n shows:
Code:
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:22
Both cases are the same rule, just one is shown "numerically" while the other has common names substituted. iptables-save, for example, will ALWAYS use the numeric form.