hmmm, one thing to try, is tell all the other machines on your network to use the internet gateway box (be it a router or a PC) as a DNS server - as they won't know about using your ISP as the DNS server. thats the gateway system's job to look after the packet routing between the Lan and Wan.
so for example.
gateway machine (router / PC / whatever)
internet connection
WAN IP supplied by DHCP from ISP
DNS IP suppied by DHCP from ISP
gateway IP supplied by DHCP from ISP
network connection
LAN IP 192.168.1.1 (and dishing out DHCP addesses from 192.168.1.2 to 192.168.1.254)
DNS IP 192.168.1.1 (as it is the DNS server from this network)
gateway 192.168.1.1 (as it is the gateway for this network)
2nd machine (PC working with DHCP) gets the addesses from the gateway machine
LAN IP 192.168.1.2
DNS IP 192.168.1.1
gateway 192.168.1.1
3rd machine (amiga wanting a static IP) set it to a high IP address in the IP range, so there is little chance of it being re-allocated by the gateway device
manually set the
LAN IP 192.168.1.100
DNS IP 192.16.1.1
gateway 192.168.1.1
to summerize, set all your LAN machines to have the DNS address set to the gateway machine's IP address.
--edit--
i've never known a router not DHCP its entire range (2-254), unless it was configured not to.
my router is set to DHCP from 2-99, amigas being static on 100 to 199, and static server addresses on 200-254
