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.)
Re-associate batch of dead tracks with files from selected folder
Export artwork of selected tracks to parent or specified folder
Delete characters from the beginning or ending of selected tracks' name, artist, album, comments, composer, or show tags
Locates pairs of track entries pointing to the same file
Remove iTunes tracks disassociated from files
Display, create text file listing info of dead tracks