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.)
Set choice of various number tags of selected tracks incrementally
Change video kind and video related tags of selected video tracks
Export files of tracks in two or more playlists to single folder
Export album artwork as folder.jpg to Album folder
Edit a selection of iTunes tracks' tags "old-school"
Enter text for the selected tracks' Description tag