My guess would be using gimp or photoshop and pasting the images on multiple layers. <3

:P i tried gimp and I could not get it to import another picture into a different layer

Aww :< Im sorry...

search torrents for a collage maker?

Last resort... Draw each picture individualy (duh) and paste them to paint and cut what you want. Then open a new one and paste it there. Repeate, pasting your drawings onto the finished product.

What? Thats what getto old me did.

I actually tried that, but it would not let me copy the content from one window and paste it into another :P

Oh? Really? Thats odd... Well, i cant really help. XD

I wish you the best of luck. ^^