In each case, the archives are in one hour sections, and are listed in reverse chronological order. So, the most recent show is right at the top. But, if the show takes up two files, the first one that you want to listen to would be the second one listed. The dates and start times of each segments are listed. You can click on the little triangle for streaming audio, or you can select 'Download Audio File'.
The tricky one is In The Pines. The first half hour of that show is actually the second half of the second One O'Clock Jump download file. I hope that makes sense! Give it a try. You'll see what I mean.
Some older shows that were archived with a different system are listed below. Again, click on the li'l triangles to start playback.