For parallel adapters, you can use the ddrmat.o driver available at http://icculus.org/pyddr/ddrmat-0.12.tar.gz
(which is a modified gamecon.o from the 2.4 kernel). Once compiled, just run insmod ddrmat gc=0,7 (where 7 is the IRQ of your parallel port, which is probably 7). Note that your lp (parallel printer) module cannot be loaded at the same time. The normal gamecon.o module might work too, although you may have to rotate your pad 45 degrees.
USB drivers are much easier. If your kernel has USB joystick support, just plug it in and it should work. If it doesn't, make sure the input, hid, and joydev modules are loaded (the first two are required for any USB input device).
If it is a USB2 connection and the above doesn't work for some reason, you may want to check to see if you
have the 'hotplug' krenel module installed. I found I needed this for an Que! External USB2 CD-RW drive I bought.
Hope this helps
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