Today, we all use IP-level networking without even thinking about it. IP  has an address scheme that is laid on top of the LAN (in the vast majority of cases, Ethernet) addressing scheme -- in this case, IP addresses.

In previous years, many DOS and then Windows applications  used NetBIOS (later called NetBUI) as their network. This was originally a non-routed protocol, a sort-of layering on top of Ethernet frames. The addressing was accomplished with a server that handed out a cross-reference of "You want to talk to this NetBIOS node? Here, talk to this Ethernet address."

Officially, NetBUI is not supported in XP, but the components are available to support it.

So my next question would be "is the accounting app trying to use NetBIOS for networking?"