Create strip from image sequence

I need a script or action, or droplet or something that will take a folder of images and create One Image strip from it. Basically I have animations I have rendered out as frames that I need to put in a game. The game needs the images in one file with all the images side by side (or on top of each other I think) The frames are all one size (but different for each sequence) It takes about 4 hours for me to do this now. And then if it has to change it's four more hours...

Any thoughts idease or techniques?

C