You don't need an iPod, just iTunes and a compatible player.
Decide which songs you'll want to adapt (the way I selected mine was tempo/energy - I put "walk" or "run" in the comments section so that I can then sort all my songs by comments and find them quickly. I wanted up-tempo peppy songs to walk to, and really high energy, driven songs for running).
Click on the individual song, click on "File" then in that drag-down menu click "Get Info".
From there, you'll click "Options" (and once you've done that, that screen is the one that will show up from the "Get Info" tab, I think as long as iTunes is open, or it might be a reboot of the computer thing...)
In the Options screen (of "Get Info"/"File") you'll see a "start time" and "stop time" option.You can punch in any times you want.
It may be easiest to just start at the beginning of the song and go out sixty seconds (or whatever the time) but listen first - many songs start with a few seconds of nothing, or very slowly build up, or have different tempos in different sections (if you were to run to "Bohemian Rhapsody", for example, you wouldn't want the funky mystic-y section in the beginning, you'd want to start where it really starts to kick)
Once you're done with that time, you can un-adjust the times easily back to the entire runtime of the song.
(oh, and while we're on the subject, The Who's Baba O'Riley is the perfect time and a great energy for a warm-up walk as is, no editing required..
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