we have a 5 public IP addresses. What we basically want to do is have a router(one single router) that will translate a static private IP so that it uses a static public IP(as in, NOT the gateway public IP)
Is this possible to do without multiple routers/nic cards(more than 2 nic cards)?
For example: say we have 3 computers 192.168.1.2-5 well we want for 192.168.1.3 to have the static public IP of ..*.1 where our gateway has *.6.
Basically, it would be setup so that whenever someone does a ping from the internet to ..*.1 it would come through the router and be routed to our computer 192.168.1.3. And also for all outgoing traffic from 192.168.1.3 it is marked as going out from ..*.1
As Kyle said, yes, this is possible depending on what you're using for your router. Since you didn't mention a specific model/technology, I'll assume you haven't chosen a router yet. In that case, I'll recommend Pfsense. It can run on a spare PC you have sitting around or altertatively, one of several low-voltage embedded platforms. PFSense is based on FreeBSD, and as such is free (beer) and free (speech).
In PFsense, you can set up "Virtual IPs" on the WAN interface - these can be natted through to the lan via 1:1 NAT or 1:N NAT, depending on what your needs are.
This is possible to do as you describe, you will just need the right router software to do it.
The real question is whether or not your router is capable.
That feature is normally called "1 to 1 NAT". Look for that in the documentation of whatever routers you consider. Domestic routers don't normally have that feature, but any open-source or corporate grade router should be able to do it; all the BSDs and Linux have that feature in their kernels.
Personally, I'd use a Linux-based router with a recent Shorewall firewall package (you do want some security, right?), that can certainly do it. In fact, I just did that using a used server, with Ubuntu 9.10 and the latest Shorewall. OpenWRT should let you do it pretty inexpensively.