Irfanview (freeware available at just about every shareware site) would be the easiest. It will resize everything in a directory as well as allowing other changes (dpi, brightness, sharpness, etc.). The keyboard shortcut is hitting B, Add All, and Start. You'll first have to set the Advanced Options to allow changes to image sizes, but it remembers those settings for other batches.

It's not that hard to do batch actions with Photoshop. Start a new action, click record, do all the things you want, hit stop, and then run it through the Batch command on the file menu.

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon