In PS CS3, load the images as a stack, and use the animation pallette to set timing and sequence. The trick is to then save it using
Save for the Web and Devices to save it as an animated GIF. That's the only was in CS3 that I've found to make an animated GIF.
In PS CS2, and earlier versions I think you do all that in Adobe ImageReady
... my memory could be a bit rusty here and I don't have access to it ATM to check...
Al.