Xircom released several parallel port Ethernet adapters, and the advantage to these adapters is they can add Ethernet capabilities to any PC compatible with a standard parallel port. They work better with bidirectional and EPP ports, but will function on a standard unidirectional port quite well. Intel bought Xircom, so it hosts the drivers for the PE3 series of adapters here : http://www.intel.com/p/en_US/support/highlights/network/pe3
When it came to the PE3 series, Xircom released four adapters :
PE3-10BC - Twisted Pair (RJ-45) and Coaxial (Thin Ethernet) connector
PE3-10BT - Twisted Pair (RJ-45) connector
PE3-10B2 - Coaxial (Thin Ethernet) connector
PE3-10BX - AUI 15-pin connector
If you get one with only a Coaxial or AUI connector, you will probably need an adapter for the Coaxial connector or a transceiver to add an RJ-45 port to the AUI connector. These are usually $10-20.
Sometimes these adapters come with a wall-wart, other times with a "Phantom" PS/2 power cable. If you have the Phantom cable, do yourself a favor and throw it away. It is intended to plug into only into a PS/2 mouse port, but the power draw of the adapter may cause damage to the adapter or the system.
The official AC power adapter is rated for DC output at 12v/500mA. This will be sufficient for any of the above adapters. A 300mA adapter will work with all but the BX. If you need a wall-wart, buy one like this : http://www.radioshack.com/product/index.jsp?productId=3832491 You will need the "N" Adaptaplug, which should be provided in a store at no extra charge. The adapter uses a positive tip, so the + symbol must be next to the TIP symbol on the tip end.
Never insert or remove any device from a parallel or PS/2 port when the computer is on. Install the Xircom adapter when the computer is off and plug in the AC adapter for the Xircom before turning the power on.
Once installed, the installing the packet driver in DOS is simple, and usually all that is required is designating the software interrupt and setting the mode to unidirectional or non-EPP bidirectional if your parallel port does not support a bidirectional or EPP port.
There is a previous PE2 series, with at least a 10BT, 10B2 and 10BX. Drivers for those adapters can be found here : http://www.minuszerodegrees.net/manuals.htm