Question About Sizing Grainy Photos

I scanned some photos from W magazine. The photos are very grainy at 100% in both PS and PSP. At 25% they are beautiful and if I change the size to 100x100 pixel, it becomes very tiny. If I change the size to 100x100 pixel when it is at 100%, it's still very grainy. How can I get the photos to icon size without the grain? Any thoughts?

Thanks in advance!