Newbie Question about IVM

I am pretty good with computers and I am looking for an inexpensive way to do automated outbound phone messages (Interactive Voice Messaging) for a small community organization for which I volunteer. Can you provide some guidance? I have an old Pentium 733 mhz (though I can get something better), am thinking of attaching to a single phone line via Comcast, and am looking for an inexpensive telephony card and software. If you have some ideas, know of an easy “how to” manual, or can point me in the right direction, that would be fantastic Thanks in advance for you help.