2. Hardware required to use PLIP.

The hardware required to set up a PLIP interface is (obviously) a free parallel port in both the machines and the cable. If you can configure it with your BIOS, set it at least as "bi-directional", but if possible in ECP or EPP mode.

About the cable, this is what is written in the plip.c file, in the kernel 2.0.33 source:

  The cable used is a de facto standard parallel null cable -- sold as
  a "LapLink" cable by various places.  You'll need a 12-conductor cable to
  make one yourself.  The wiring is:
    SLCTIN      17 - 17        
    GROUND      25 - 25
    D0->ERROR   2 - 15          15 - 2
    D1->SLCT    3 - 13          13 - 3
    D2->PAPOUT  4 - 12          12 - 4
    D3->ACK     5 - 10          10 - 5
    D4->BUSY    6 - 11          11 - 6
  Do not connect the other pins.  They are
    D5,D6,D7 are 7,8,9
    STROBE is 1, FEED is 14, INIT is 16
    extra grounds are 18,19,20,21,22,23,24

In my opinion you should avoid building your own parallel null cable. A self-made cable may save very little money, but can add lots of headaches. If you wish to build your parallel cable, remember that you're doing it at your own risk, I reported exactly what is written in plip.c but I don't give warranties.

A final word about cable length: long cables (i.e. more than 10 feet or 3 meters) may bring problems due to radio interference. If you need long cables you should use good and well shielded cables, but very long cables are not recommended: I think the maximal cable lenght should be 15 meters (50 feet).

Anyway, someone mailed me that his/her 100 feet (30 meters) cable works fine; if someone really wants to try a PLIP connection between the office and his/her home (200 meters away), and has the money to spend, can try it, but is at his/her risk.