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.)
Remove iTunes tracks disassociated from files
Perform search-and-replace on text in your choice of tags
Change video kind and video related tags of selected video tracks
Change file type to make selected AACs bookmarkable
Deletes the lyrics of every track in the Music playlist
Make a text file listing Albums that have some/no tracks with artwork