I'm not sure about PS, but I have PSP, and although I can't do a bunch at once, what I CAN do is open them all, then set my crop tool for 4x6, and just go through each picture and apply the crop to them. It's actually pretty quick. Just don't forget to Save As new or you'll have to do it all over again.
If you want the actual photo to be RE-SIZED, I'd do the same thing - open them all up, then, after applying the resize to the first photo, use whatever keyboard shortcut PS uses (PSP's is ctrl+y) on the remaining ones.
HTH!