Sure, iTunes can join tracks, but only if they're consecutive CD tracks, and you haven't imported them. This script allows you to join any two (or more) MP3 tracks (repeat: MP3 tracks only), provided that they are the same format and bitrate.
Also see Join Together, an application that will join any type of files.
(Note: In order to launch this PowerPC-era script on an Intel machine, it must first be opened and then saved using AppleScript Editor, which is located in your /Applications/Utilities/ folder. More information is here.)
Create text file listing tracks common to and exclusive to two playlists
Change file type to make selected AACs bookmarkable
Copy selected CD's CD Text to the clipboard
Search Wikipedia using the Song Name, Album, Artist, or Composer of selected or playing track
Rename selected tracks' Song Names with their filenames (minus extension)
Exports and then re-imports selected tracks' artwork