How do you setup NAT ?

If you're talking about Linux, you need to look into iptables. Here is the NAT section of my firewall script that I use here at home:

iptables --flush
iptables --table nat --flush
iptables --delete-chain
iptables --table nat --delete-chain

# Set up IP FORWARDing and Masquerading
iptables --table nat --append POSTROUTING --out-interface $EXTERNAL -j MASQUERADE
iptables --append FORWARD --in-interface $INTERNAL -j ACCEPT

echo 1 > /proc/sys/net/ipv4/ip_forward

Just replace $EXTERNAL with the name of the interface on your Linux box which connects to the internet, and replace $INTERNAL with the interface that goes to your internal network.

If you're talking about Windows, then you just need to use Internet Connection Sharing.

i am not talking about iptables , i am taking about assigning private ips like 192.168.0.xxx to my servers , but the private ips must be linked with public ips.

ip addr add 192.168.0.xxx dev your_device

i dont mean how to add address or bring up ips on the servers. rather how do i link the private ips to the public ips ?

Are both sets of IP's on the same server? If so, you'll need to forward whichever ports you need from the external IP to the internal IP, probably by using IPTables (though I've no experience of this)