Typically, most taps can get away with just a series resistor and a series cap. The resistor provides a modicum of isolation between the computer sound card audio input and the radio receiver's discriminator output that the tap is connected to which prevents the sound card from "loading down" and severely affecting the discriminator circuit. The cap is used to provide blockage to possible DC current that might be present on the discriminator output. Neither is always necessary - it depends on the receiver and sound card designs but that basic arrangement is usually a good "best practice" to follow. Having no components at all in line of the tap does mean that the full bandwidth of the discriminator output is present on the line so this provides the maximum flexibility for attempting a wide range of demodulating differing types of signals.
Using two resistors instead of one is usually done in the form of a "voltage divider" arrangement - this is usually for "stepping down" the audio amplitude coming from the discriminator in case it is too hot for the sound card to handle. In such a case, the smaller resistor is shunted to ground at one end while the other end is attached to the series resistor coming from the discriminator (the end of the series resistor not attached to the discriminator - the end facing the sound card input). In the reverse of this - larger resistor shunted while smaller in series - it is likely more for providing a more optimum "resistive load" to either the sound card or discriminator.
In most cases, a series 10K resistor in series with a large (1uF or more) cap usually works fine and only needs to be altered if amplitude (audio level) and/or frequency (signal bandwidth) issues need to be addressed. I have a tap on my old Pro2052 which is "naked" - no isolating components, resistor or cap, in line and it has worked fine using many different sound cards. Still, if unsure, it's best to at least put the series resistor (10K or so) inline.
All of this can be done either with or without mounting components on a perf board or PCB - just directly soldering them together with the cable. Using a board, especially when using three components in the voltage divider setup, yields a cleaner look and better mechanical stability. When only one or two series components are used, you can usually get along fine by simply soldering the components together and then either wrapping some electrical tape around them (to prevent shorting) or using heat shrink tubing.
-Mike
