Problems removing rules

["Maurício S. Mudrik" <mudrik@intercomax.com.br>]

I'm having a huge problem:

I have those rules:

Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination
DNAT       tcp  --  anywhere             anywhere           tcp dpt:www 
to:192.168.0.1:80

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
MASQUERADE  all  --  anywhere             anywhere

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

I inserted iptables -t nat -I PREROUTING -s xxx.xxx.xxx.xxx -j RETURN

OK. The rules works fine.

Then I removed the RETURN iptables -t nat -D PREROUTING -s xxx.xxx.xxx.xxx -j 
RETURN and... The IP still access some pages that accessed before!

Why?

I need to redirect all internal requests to a specific page and then, after a 
login, masquerade them to the Internet...

That's it.

Thanks in advance.

Maurício S. Mudrik