Why not create a Playlist in iTunes with the tracks you want to sync the iPod to? Then hook up the iPod, and on the Music tab in the device profile screen, check Sync Music, and then also click on Selected Playlists, Artists, Albums, and Genres.
Once you have made those two selections, you will see a list of Playlists, Artists Albums, and Genres in separate groups below the options. Select only the Playlist you created leaving everything else unchecked.
Then sync. When you sync, you will get the Playlist only downloaded.
You want to make sure your friend understands that once you do this, he will not be able to sync Music on his own computer. If he tries to sync to his own computer, it will erase all of the music you have downloaded for him.
Is your friend not planning on syncing his device to his computer anymore?
Another option would be for you to copy the selected tracks to a flash drive or CD so that he can load them into his iTunes library. That would be a much cleaner way to do the entire thing....
If you're using an iPod classic, you should be able to connect to and transfer non-DRM music from iTunes on multiple computers and NOT have it erase what's on the iPod. I routinely for my iPod Mini, 5th gen Classic and 7th gen Classic with no trouble.
BUT it will need to be in 'Manually manage music' mode. I had to admit that I don't haven't used 'Sync' mode since I figured this out years ago, so can't say for sure, but In a sense, it wants to ‘equalize’ the iPod to the computer and the iTunes that it’s connected to. So, if the computer you’re connecting to is not its main one, it will want to erase and start over and Sync to that computer.
Manually manage music is the way to go.
You SHOULD be able to get it into Manual Manage mode by connecting the iPod to your iTunes and saying 'NO' to 'Erase and Sync.' Then click on the main level of the iPod where you’ll see the picture of the iPod, its name and capacity, etc.
Above the iPod’s picture, you should see “Summary,” “Music,” “Movies,” “TV Shows” and on and on…
You should be able to click “Music” and see a check in the box that says, “Sync Music.” If you uncheck that box, it should put the iPod into Manually Manage mode.
It MAY still make you erase the music that’s already there (I’m sorry, I just can’t remember right now), but after that, you should be able to connect to any iTunes and pick the songs you want from the library and drag it onto the iPod.
Just a clarification on the Maunal Sync that bwhite has explained:
It MAY still make you erase the music that’s already there (I’m sorry, I just can’t remember right now), it won't - once you say No to the Erase and Sync, the device profile screens display, and you can check Manual Sync as bwhite has indicated.
but after that, you should be able to connect to any iTunes and pick the songs you want from the library and drag it onto the iPod. The Manual Sync selected for the device on that computer will apply only to that computer. Each different computer that you hook it up to has to have the device profile set up for that computer. This design allows you to have different profiles for different computers. For example, on my husband's Macbook Pro, we have our devices set up to sync to everything but Photos, since that is where our iTunes library lives. On my Macbook Air, we have our devices set up to only sync with photos, since that is where our iPhoto library lives....
Thanks to all for your help. Somehow, mysteriously overnight the music got deleted from my friend's iPod (maybe I was smarter than I thought). And I've sucessfully added a new playlist.
Now I am trying to get the songs to stop after each one is done without automatically starting the next one. I've just put up a new question about that in the discussion forum.