I am using netgear ADSL router connected to internet and my LAN,
I have configured remote desktop for my server and is working fine, but I need to configure remote desktop for another workstation, I am having only one IP address,
When I try to connect it connects only to the server.:o

For something like this you'll need PNAT (Port based Network Address Translation). Check to see if your Netgear can do that and if it does then setup 2 different ports that map to 3389 on each of your internal machines.