Iptable

Well your question is not particularly clear but if I understand it correctly then the answer is as follows:
1. I assume that your router is doing some kind of NAT to convert your 1918 IP on your linux box to a real ip, so under that assumption all we need to do is to convert the 192.168.2.x address to 192.168.0.x and push it out eth0 and the router will do the rest. If that is the case then a line like:
iptables -t nat -A POSTROUTING –s 192.168.2.0/24 -o eth1 \
-j SNAT -to 192.168.0.8
should do it.
2. You need to intercept the request before it gets processed so something like this should work:
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8080
assuming that the device that is running the iptables is also the one that is running the proxy.

Which sentence put first iptables -t nat -A POSTROUTING –s 192.168.2.0/24 -o eth1 \
-j SNAT -to 192.168.0.8
or  iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8080

iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j REDIRECT --to-port 8080

note I spotted an earlier mistake I made, change the -i eth0 to -i eth1 as in the above line

why not simply using:

iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

Flushing firewall rules:                                   [  OK  ]
Setting chains to policy ACCEPT: nat                       [  OK  ]
Unloading iptables modules:                                [  OK  ]
Applying iptables firewall rules: iptables-restore: line 1 failed          [FAILED]

I copy  iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE   into  /etc/sysconfig/iptables   on FC2
and  run   service iptables restart   result is above

This is my  /etc/sysconfig /iptables    
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

it have  only 1 line