First select all the songs from the medley, and press Control-I to open the Get info box. In the "Grouping" field type in "Abbey Road" or whatever you like. Press OK, this will add the grouping info for all the songs.
Now you need to go to iTunes' Preferences->Playback and select "Shuffle: Groupings" (instead of songs or albums). Here's the description of how this works from iTunes Help:
"To choose whether iTunes shuffles individual songs, complete albums, or groupings, choose iTunes > Preferences, then click the Playback button. Select Song, "Complete albums" or Grouping. If you select "Complete albums," or Groupings, iTunes plays the songs in the order in which they appear on the album or in the grouping, and then chooses another album or grouping randomly."
First select all the songs from the medley, and press Control-I to open the Get info box. In the "Grouping" field type in "Abbey Road" or whatever you like. Press OK, this will add the grouping info for all the songs.
Now you need to go to iTunes' Preferences->Playback and select "Shuffle: Groupings" (instead of songs or albums). Here's the description of how this works from iTunes Help:
"To choose whether iTunes shuffles individual songs, complete albums, or groupings, choose iTunes > Preferences, then click the Playback button. Select Song, "Complete albums" or Grouping. If you select "Complete albums," or Groupings, iTunes plays the songs in the order in which they appear on the album or in the grouping, and then chooses another album or grouping randomly."