1. Place the video &audio from the first tape on track 1&2. 2. Place the video & audio from the second tape on track 3&4 3. Then use the "Video Level" under "Object curve effects" to dissolve between the two videos. For details on using "Object curve effects" please see the How-to Tutorial for Movie Edit Pro on our support site.
Since I don't know what software you have, these instructions may not apply. In this case please contact our support.