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
Change video kind and video related tags of selected video tracks
Perform search-and-replace on text in your choice of tags
Display, create text file listing info of dead tracks
Append user-entered text to beginning or ending of selected tag of each selected track
Remove iTunes tracks disassociated from files