Help with a programming problem

I've been trying to do this for ages now, and it seems like it should be something with a really simple and elegant solution, but i can't find it. 

The problem:  I have a series of images, all with the same dimensions.  I am using two templates in order to combine these images into 1 overall image.  The two templates are as such, one combines them horizontally, one vertically. As images are combined, they are scaled appropriately to fit the canvas, and a number of iterations of these templates can take place. Link is to visual example of this.

http://img230.imageshack.us/img230/4391/templateexamplewa6.jpg

I've managed to somewhat acheive this through image manipulation, but i need to do it via sheer maths (processing speed).  An added problem is that like in iteration 3, there are 3 images in the row. They should all be 33% of the canvas width each, and image 2 should be 66%. 

Any help would be greatly appreciated, it has made my head hurt.  It's also possible my explanation blows, so feel free to ask questions.

>>4

What you seem to be suggesting there is what I initially first tried - the image manipulation route.  Unfortunately this is impractical due to the time it takes to process, copy, paste, etc.  That is, if I've understood you correctly.

But thanks for trying anyways.

>>3

Just read it, and I'm not 100% clear on how this solves my problem.  I found it pretty hard to follow in general actually, could you elaborate on how this fits in?