parallel jtag
The question is "not only" to glue some hardware together. Which kind of software do you want to apply to this interface?
e.g.: the Software development package from STM for ST20 procesors (ST20 Toolset) supports only their own hardware. To use ANY (self-build or commercial) different hardware, you need at least to write your own device driver to be able to communicate with the different interface.
There is some kind of "very simple" unbuffered JTAG interface for PC´s parallel port available, which may be set up (dependent of the effort you want to spend) by only some resistors, or (better electrical characteristics) with some TTL driver chips. This Interface will be used by the popular software "JKEYS".
But nevertheless, as far as I know, there is no software driver available, which may help to use that simple "Wriggler" interface in conjunction with ST20 Toolset.