Scrolling background help

hi everyone,
i have a problem with an effect i would like to create.
if you look at the link below you will see 3 buttons. for each button there is a co-ordinate specified of the background.
http://geocities.com/spidermassi2004/sfondo_scroll/
what i am looking for is a way to have the transition between one co-ordinate and another one.
i hope someone can help me.
thanks in advance

for each button the code is:
on (release){
foto_mc._y = -1500
foto_mc._x = -1000
}

where foto_mc is the movie clip containing the picture of the background

i hope someone can help me.
thanks in advance

Spidermassi