Well, in this amount, my best recomendation is something I use to resize images before I give them to the client. I have created actions within Photoshop, one called "Vertical" and one called "Horizontal" obviously simplifed, where it will open the image, change one deminsion, and the resolution, save it, and then close it. To do a large amount, which, while I do, but not in your higher quantity (it would still work though, just take longer) but what I do after that is copy them to my desktop (total seperate copy in case I screwed up) and then go to "File - Automate - Batch" where another window will open with several options, just make sure you select the new folder on your desktop. Maybe create a second destination folder as well. I hope this helps in some way.
I know that I am one with beauty, And that my comrades are one. Let our souls be mountains, Let our spirtis be stars, Let our hearts be worlds.