Can a network is run without IP numbers?

I have little knowledge (not for long) about WinXP. I went to a location where they have one Win98 PC and two WinXP (in such a brief visit, forgot if it was Pro or Home edition) pc’s. The only network info on the Win98 PC is the workgroup name. It has no IP’s assigned at all, yet can view the other computers. Is XP acting as a DHCP server? If that is the case, how do I tell which one it is? Never have done much work with DHCP (and don’t know why someone would set up a small network with it being it uses dial up net access).

Any advice is appreciated.

Thank you!