You start by going to your local Radio Shack and getting a cable that will plug into the headphones jack on the tape player and then to the Line-In jack on your sound card. Shouldn't cost more than a few dollars. The important thing is making sure you have the correct jack size, which is typically 1/8".

Once that's done, you'll need an audio recording program, and a lot of free disc space. You'll most likely have to first record the audio in WAV, or uncompressed, format. At 45 minutes long, that'll take probably around 500MB. After which, you can convert the WAV into an MP3 or any other audio format you want, and since it's a speech or presentation, you can get away with a low bitrate on the encoding as well as the frequency sampling. Something like 32 or 64Kbps at 22.5KHz shouldn't detract much from the clarity of the person speaking (it'd be like the difference between FM and AM radio) and will cut the resulting file size down considerably. You might get it under 100MB at such settings.