Another option would be to login to the router and assign a static IP Address to the copier. When setting an IP Address straight from the copier, there is still a chance the router can assign the same IP Address to another computer, therefore causing the printer to have an IP Address conflict with another device. This might be what's going on. My other guess is that the copier is trying to pull an IP Address from a range other than the router is using. For example, the router might be assigning addresses from the 192.168.0.1 - 192.168.0.100 range, when the copier has something like a 192.168.1.3 address. In this case, the computers won't be able to see it without some tweaking.
Can you get the Brand and Model # (including version, if applicable) from him and let us know?
Can you also find out the default gateway his computer is using?
1. Go to Start Menu
2. Go to Run
3. Type "cmd" and click OK
4. In the black box, type "ipconfig" and press Enter
5. Let us know what it says for default gateway
Meanwhile, I'm sure a few of us will be looking for a manual for that copier. There's probably a System menu with a TCP/IP Config screen (or something similar). :)