So the mystery 3com router on a floating DHCP address was actually the one in the TCS lab. I've given it an IP now listed on the ATF wiki.
The 3com switch that was unaccounted for is actually the one in the PSL lab. I've tried all the IP addresses it should be and it is compleatly unresponsive. Local devices that have been configered with manual IPs are accessing the wider network fine but anything set find an IP via DHCP is failing to get an IP address. We can't chage any of the settings unless we know the IP of the router.
Jon is similtinously working on getting a gateway PC up and running, but the only change there is that the main 10.0.1.1 router has been disconnected from the wall. I'll try running a deeper nmap scan over the PSL side of the network to find this 3com router.