There are several ways to put your laptop on a network. You can use the SLIP code (and run at serial line speeds); you can get a notebook with a supported PCMCIA slot built-in; you can get a laptop with a docking station and plug in an ISA ethercard; or you can use a parallel port Ethernet adapter.
This is the cheapest solution, but by far the most difficult. Also, you will not get very high transmission rates. Since SLIP is not really related to ethernet cards, it will not be discussed further here. See the NET-2 Howto.
Try and determine exactly what hardware you have (ie. card manufacturer, PCMCIA chip controller manufacturer) and then ask on the LAPTOPS channel. Regardless, don't expect things to be all that simple. Expect to have to fiddle around a bit, and patch kernels, etc. Maybe someday you will be able to type `make config' 8-)
At present, the two PCMCIA chipsets that are supported are the Databook TCIC/2 and the intel i82365.
There is a number of programs on tsx-11.mit.edu in /pub/linux/packages/laptops/ that you may find useful. These range from PCMCIA Ethercard drivers to programs that communicate with the PCMCIA controller chip. Note that these drivers are usually tied to a specific PCMCIA chip (ie. the intel 82365 or the TCIC/2)
For NE2000 compatible cards, some people have had success with just configuring the card under DOS, and then booting linux from the DOS command prompt via loadlin.
Things are looking up for Linux users that want PCMCIA support, as substantial progress is being made. Pioneering this effort is David Hinds. His latest PCMCIA support package can be obtained from:
Look for a file like pcmcia-cs-X.Y.Z.tgz where X.Y.Z will be the latest version number. This is most likely uploaded to the tsx-11.mit.edu FTP site as well.
Note that Donald's PCMCIA enabler works as a user-level process, and David Hinds' is a kernel-level solution. You may be best served by David's package as it is much more widely used and under continuous development.
Docking stations for laptops typically cost about $250 and provide two full-size ISA slots, two serial and one parallel port. Most docking stations are powered off of the laptop's batteries, and a few allow adding extra batteries in the docking station if you use short ISA cards. You can add an inexpensive ethercard and enjoy full-speed ethernet performance.
The `pocket' ethernet adaptors may also fit your need. Note that the transfer speed will not be all that great (perhaps 200kB/s tops?) due to the limitations of the parallel port interface.
Also most tie you down with a wall-brick power supply. You can sometimes avoid the wall-brick with the adaptors by buying or making a cable that draws power from the laptop's keyboard port. (See keyboard power)
See DE-600 / DE-620 and RealTek for two supported pocket adaptors.