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.)
App displays files in iTunes Media folder which are not in iTunes library
Renumber order of selected tracks
Append user-entered text to beginning or ending of selected tag of each selected track
Copy Artist to Album Artist of selected tracks
Enter text for the selected tracks' Description tag
Move selected playlists to a new or existing folder