How can i measure if a movie clips X value is increasing?

Hi… thanks for your patience, im new to this forum but have been visiting the site for years to find flash tips and tutorials… i really appreciate any help you guys can offer.

Here is my dilema…

i have one MC_PANEL.
inside MC_PANEL are a series of movie clips lined up horizontally called MC_1,MC_2,MC_3 etc…

MC_PANEL can be scolled left or right to access all 50 of the included movie clips. Whenever you roll over an MC_#, an image is displayed in the center of the stage.

That whole part i can do no problem… what im having trouble figuring out is this…

I want the images called by onRollOver of an MC_# to move in from the left stop mid stage, and move out to the right IF the larger MC_PANEL is also moving left to right. And vis versa, i want the images to move into the stage right to left if the MC_PANEL is scrolling right to left.

To do this i think i need a way to assess if MC_PANEL._X is increasing or decreasing. Can anyone tell me how that might be done?

Here is what im thinking i need…

If( mc_panel._x is increasing){
mcA.attachMovie(“mcB”)
}

if(mc_panel._x is decreasing){
mcA.attachMovie(“mcC”)
}

then… another problem comes into play… how might i tell mc_1 which movie clip (mcB or mcC) it should load its movie clip to?

mc_panel.mc_1.onRollOver =funciontio(){
mcB/mcC.attachMovie(“Project1”)
}

Thank you so much for any help!