Well the new Shareaza and LimeWire support host browsing. So I guess you can enter the IP address of the other computer that is also running Shareaza and LimeWire (or any client that supports host browsing in the future).

http://www.shareaza.com/
http://www.limewire.com/index.jsp/download_beta

Gnucleus also has a LAN version, would that work?

http://www.gnucleus.net/

But why don't you just use FTP?