When in PS, open your image file. Click on window->actions
Under the actions tab, there are a few small icons at the bottom.
Click on "Create a new action", which is left of the dustbin icon. It'll start recording whatever u do. Essentially u should just resize the image, den save it somewhere. Den click on the stop button under the actions tab to stop recording. After that, u can do batch processing for all ur pics under File->Automate->Batch. Choose the source folder and the folder to save to, and of coz the action u have just saved and ur done =) Not sure if the action will work for both portraits and landscape pics though.
Hope this helps