Home Automation Systems, Inc. sells all the equipment you need to control a TV, stereo, or any infrared remote-driven device from your PC:
Home Automation Systems used to sell a developer's manual that told how to communicate with One-For-All remotes through a serial port. I've heard that they no longer sell it. Hopefully the information on this web site and others provides all that you need.
Several people have successfully programmed Macs and PCs to communicate with OFA remotes. The serial protocols described here pretty much cover how to get the remotes talking, but the codes are often totally different, depending on the model.
Zig has not written any software to communicate with his OFA-6. Zig has the attention span of a ferret on meth, and before Zig could finish, Zig was distracted by a shiny object and forgot all about the IR/Mac project.
Even though Zig never wrote any software or built any hardware for computer-controlled IR remotes, Zig still gets 2-3 questions a week, and Zig's glad to answer them.
Many thanks to all the helpful people who have sent in code snippets, applications, and even serial cable schematics. You have all contributed to the collective knowledge here, and this site owes its current existence to your continued interest.
The US$20 serial cable that Home Automation Systems sells has a small printed circuit board in the male DB9 connector housing. If you want to build your own cable, you might try this schematic that one kind author sent Zig.
One person wrote me saying that it's possible to just solder wires to the remote's serial port, and poke those wires into the Mac DIN-8 serial port. Since one person did this successfully, it must work. Zig isn't so trusting: the Mac serial port has peak-to-peak voltages far in excess of what the remote is looking for, and might cook some component on the remote control.
Before spending a long time programming your remote, consider replacing the batteries with something that will last for a while.
Newer 9600 baud protocol: