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.)
Exports and then re-imports selected tracks' artwork
Convert or import tracks with any encoder on the fly
Remove iTunes tracks disassociated from files
Rename selected tracks' Song Names with their filenames (minus extension)
Re-associate batch of dead tracks with files from selected folder
Export album artwork as folder.jpg to Album folder