You use single RJ45/UTP/CAT5 crossover to connect two network cards directly or use two regular straightthru if you have a hub or switch/router in between. Share it using a LAN ip like 192.168.1.x 255.255.255.0 and use the TCP/IP or Windows File Sharing
A modem connection would be a serial connection and it's gona be slow. Not seen anyone use it since Doom and Laplink pre millenium era! I think it identifies it's self as Com1 or Com2. again you need a special crossed over cable for the job.
DinoHunter (still no nVidia compo voucher!), CPU/GPU Benchmark, DarkFish Encryption DLL, War MMOG (WIP), 3D Model Viewer