segmenting home network for testing

Here is what I would like to accomplish. I want to setup a separate segment on my LAN for testing out new exploits, tools, etc. and still maintain the current segment for general use. I would like to be able to get out to the internet on my test segment to download patches, apps, etc. However, since this segment will most likely contain unpatched systems, I am worried about others also exploiting these systems to gain access into my LAN. What would be the best way to go about setting up this configuration? iptables, port forwarding?? I have a Dlink 625 DIR that I am currently using as a router as well as a Linksys WRT54G running OpenWRT.

I have a segmented home LAN. I have an internal network and one computer that runs a proxy that provides internet access to the rest of the computers on the internal LAN. Without the proxy up none of the internal LAN computers can hit the web (except of course the gateway). This required two LAN cards in the gateway.

the proxy is a free program fro analogX