DNAT: forwarding all ports to a host

One requirement for a firewall setup I am working on is the ability to forward 
all (remaining) ports to a specific host on the network.  Note that I am hoping 
to avoid using this but it is required as an option.

The server/router runs some services.  There is a chain of RETURNs for those 
services.  Packets with the remaining destination ports fall through to the 
actual DNAT target:
# iptables -t nat -A PREROUTING -i eth0 -j DNAT --to-destination 192.168.2.10

But what affect does this have on ESTABLISHED,RELATED connections?  Does this 
interfere with, say, a reply from google.com:80 to network host 192.168.2.99?

Links etcetera welcome.

Thanks.

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