You can use a null modem cable so you'll no longer need the RJ11 or the modems.
What you can do is this:
1. Connect your computers using a laplink cable or an RS-232 null modem cable thru your serial ports at the back of your PCs (either DB9 or DB25 connector ports). The cable can be bought from your local computer or electronic stores.
2. Then you can run LapLink software or Windows DCC (Direct Cable Connection) to make the actual system interconnection.
3. Now you can transfer files.
But my suggestion is this:
1. Get a network card for each PC.
2. Connect them thru a crossover UTP cable.
3. Set up each PC to have an IP address of say like 192.168.0.1 and 192.168.0.2.
4. Make them members of the same workgroup.
5. And presto! you got a good fast working LAN!