Loop through images - code correction required

programming flash
1

Hi folks,
I am new to AS, but have spent some time traversing these forums to teach myself.

I am trying to loop through a series of images in my library that are all linked as follows:
image_01
image_02
image_03
image_04
etc

I want to loop through each of these images automatically. There are two parts I need help on.

1) Can someone help me correct the code below?

 
if (imagecounter = undefined)
{
imagecounter = 1;
} else {
imagecounter = imagecounter++
}
currentImage = "image_" + imagecounter;
currentImageNewName = currentImage + "playing";
holder1_mc.attachMovie(currentImage,currentImageNewName,1);

2) How do I check if a linked movie exists?
ie:
if (currentImage = exists) ?
Any help is very much appreciated! Thanks!

Kind Regards,
Chris