It's quite likely this "tutorial" is already known by most photo-savvy folks, but I had NO idea that this technology existed until a few months ago. I re-size every photo on my blog (and every photo on my website) to properly fit the column/size needed. Part of this is making them "web-friendly" or reducing the resolution to 72dpi so load times are not too long. These photos are NOT printer-friendly, but they look great on screens.
Before I learned this "process multiple files" trick I was re-sizing each image on it's own and it took minutes instead of seconds, which over the course of a month really adds up. I dreaded photo-heavy posts because they were so time intensive to prepare. Now I'm like, "bring it." (And I have brought it here, here and here.)
The above three minute video (click here to view full-size and be sure to let it load fully before starting) shows you how I used to process my image files one at a time and then shares my time-saving tip. I use PSE9 (I know, I know, upgrade already!) but I imagine the idea is similar no matter what version of PSE or PS you have.
I hope this helps! It was a gamechanger and time-saver for me, FOR SURE.