Sadly, the only real way to find out what is needed to make an extension work is chasing it through the inx files. Browse to the inkscape/share/extensions directory. You will find eps_input.inx which depends on ps input. In ps_input.inx you will see that it depends on sk input. And finally in sk_input.inx you will see that it depends on the on the *nix shell script sk2svg.sh. the sk2svg script calls a program named skconvert. I haven't taken the time to look this up but I would assume this is part of sketch/skencil. To make things more portable we could easily rewrite the shell scripts in a language like python or perl, though it would be IMHO much better to do that with embedded scripting since it will always be accesible no mater what the user has installed. Sketch, however is unlikely to ever run on Win32.
I think this is a great example of the power and limitations of the current extensions mechanism. It is not a script binding. A script binding will also be very useful. But in the tradition of *nix tools it allows you to combine smaller programs to get the job done. And it lets you turn almost any old program you have sitting around into an Inkscape extension.
In the end if you want eps input you need to find a path between eps and svg. If you can find a couple command line programs to get the job done, attaching them to inkscape is simple even if badly documented.
As you figure out what various extensions require and confirm that they work, please add the details to the wiki. http://inkscape.org/cgi-bin/wiki.pl?GettingExtensionsWorking
Aaron Spike