I don't know what router you are using but assuming that the router is doing your DHCP for you then I would suggest the following.
Configure the iPronto to used a fixed IP - most domestic routers will usually handle a maximum of 32 or 64 DHCP addresses within a group of 256 so that usually means there are plenty of IPs available that it won't allocate. So for example my DHCP server allocates out addresses 192.168.0.64 to 192.168.0.127 which leaves me the range of 1-63 and 128-254 as useable for fixed IPs on my network.
You'll need to configure the gateway address (which is the address of your router) and also your DNS server address (usually I make the DNS1 address to be that of the router and the DNS2 address to be 194.73.73.94 which is a BT DNS server that I just happened to pick and be able to remember easily).
Off hand I can't remember what else the iPronto needs you to configure ... don't have one handy. :-(
