Creating sprite sheets from Photoshop

Does anyone know how to take a .psd in photoshop and export the layers to a .png spritesheet, while being able to define how many rows or columns there are? Trying to create spritesheets for my 2D game. My one previous artist used to have a script that he ran (mentioned something about loading frames into a stack?) and it exported into spritesheets. We animated in Flash, and converted those files to .psds, so the frames (each layer) are already aligned.