Im running a loop and attaching multiple movie clips

can someone tell me how to then space the movieclips evenly in x and y positions ..

I need to know 1)how to space them in a grid formation

and 2)
also be able to space 3 out evenly space in x position then add another 3 after these 3 have scrolled up underneath

so the new 3mc's are spaced evenly again in horizontaly but also with an even space under the origonal 3... so they eventually make up a grid formation

Ive tried using hittest and move them etc
Thank you in advance