Try this “scratch” effect (see the second post in the topic) scratching effect
See here for how to install plug-ins: http://audacityteam.org/download/plugins
Use the “Time Shift Tool” to drag the tracks left/right so that they play one after another. http://manual.audacityteam.org/man/Tools_Toolbar#timeshift
If you keep a little overlap between them you can use the Fade-In and Fade-Out effects to make them cross-fade.