You could fight all the installation and get the proper files and so on, or go to e-bay and buy a CD that have everything preloaded, in sucha way that you could leave the CD on the computer and run the aplication from the CD, without ever installing into the machine.
You put the CD in, and in about 5 minutes you got a instant PBX, (just add a SIP phone).
From the beginning, you could dial a special number and get connected to the Digium IVR machine, using the asterisk protocol.
Many people out there already selling services, termi nation and prepaid calling cards on old P.C. with Asterisk.