Sorry, wrong tutorial. Try this one:
"Try using ffmpegX. In order to to add the subtitles you must re-encode the avi video. So, drag and drop or open the avi file with ffmpegX. Click the arrow in the area where it says "To" and select the format you want it to be encoded to. I usually choose xvid or divx. Then go to the "Filters" tab and click "Load subs" and select the subtitle file you wish to use. You can also change the subtitle font size, text style, and position (I like to keep the font size and text style default and change the position to Pos 90 to keep the subtitles a little more closer to the bottom). Before you encode the video, you can preview how the subtitles will appear by clicking "Preview." Another thing I like to do before I encode the video, is go to "Options" and check "Two-pass encoding" (this will make the output file quality a little bit better by analyzing the video and creating a log file). Once you have everything set to your preference, just click "Encode" at the bottom right corner to start the encoding process. Once its done, you should have a file, avi in this case, that will have the subtitles encoded into the video. There is no way to remove the subtitles after this process, so make sure that you don't overwrite your original avi file."
In the process of finding this quote from another forum somewhere, I also found that Handbrake can do what you're looking for.
