Apple Getting an iBook G4 on the network

At work we've got a few guys who have brough Mac's from home to use as their work machines (since they mainly only need it for email and word processing stuff).

He noticed his computer was running sluggish, so he formatted and started over, and now we can't get him on the network. (I wasn't here when he was first hooked up to the net)

So what I did was I looked at the PC next to his laptop (both plugged into the same switch under his desk) and I copied all of the details. IP Address, Subnet Mask, Gateway/Router, DNS Server, etc.

I changed the IP Address to something else in the same subnet that wasn't being used.

It still can't connect to the network. (no web browsing/email/ping'ing/etc)

Once, when I used the same exact IP as the machine next to me, it told me that IP was already in use, which showed a sign of being on the network, but when I changed it to something different it still won't let me on the web.

Am I missing something?