In this post atomickeisha__x asked how to open an animation in PS CS3, and later trekchic asked for more help, so I decided to write it here and add screenshots.
01. Click on File menu --> Import --> Video frames to layers.
02. Type *.*and click Load to show all filetypes.
03. Find your .gif and click Load again.
04. Click OK.
05. Click on Window menu --> Animation to display the frames.