Not certain which it was (I saw this off of Japanese TV recorded on Okinawa years back), but it dealt with Goku's origins. It showed his home planet and his father, along with their destruction by Freeza. Could not understand a word of what they said (well, maybe some, but not much). Still, I have fond memories of that one.
That would be Bardock: Father of Goku. Yea that is deffinatly a most exellent d.b.z. film. Good stuff. Good stuff. I need to find that one on dvd somewhere.