You have an excellent camera to work with, you just need to set the resolution. It sounds as if you are shooting at 8 megapixels (way too much for your job).
According to the specifications, you camera can provide the following resolutions.
Max resolution 3264 x 2448 (8 megapixels)
Low resolution 2592 x 1944, 2048 x 1536, 1600 x 1200, 1280 x 960, 1024 x 768, 640 x 480
Read the User's Manual and find out how to set the resolution to a lower setting. I would leave the quality setting at its best setting.
Windows Movie Maker is probably expecting 640 x 480 or maybe 1024 x 768.
I'm just beginning Stop Motion, which requires the filmmaker to take hundreds of pictures to make a movie. But I have a Nikon Coolpix 8700, which gives me pictures that are way too big for me to easily place in Windows Movie Maker. I'm taking the pics on basic quality on the camera, but they're still too big and WMM takes forever to process them. Any suggestions for a good stop motion camera? Thanks!