How can a random background function be made?

I mean Im trying - very hard - to make a game like the game "Tanks", currently Im stuck with programming on the background generating.

By that I mean EASY ways to generate random backgrounds which 'ent too impossible.

Now I dont want to generate the Y position for 400 movieclips (1pixel wide) and then getting the proximity and recheck, reposition. Thank you

THx for any help I could get.
<Tongxn>