So what's the easiest way to resize a bunch of pictures at once?

As I was going through my pictures last night, I found a bunch that I completely forgot that I had. Early Desert Storm pictures as well as boat show pictures. We have a good camera so they're all 12MB + so I have to open each picture in paint, resize to 25% and then save it just to get it to load. This take quite some times especially looking at all the pictures that I can do.

So what should I do?