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I don't think that you can do this directly in iTunes. There are some other ways to join tracks together though - e.g. in garageband. Why do you want to do this?

I guess you could also burn a CD with the two tracks next to one another then import them with 'join cd tracks' if you don't mind all the faffing about.
 
I know I could burn the tracks onto a cd and then do it but my cd burner is not currently working... we are promoting this band and want to consolidate the tracks so listeners can hear more than just one song... I guess I could send the tracks to someone and have them set it up too...
 
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