You will need to resize your photos in Photoshop Elements.
You can do this to an entire batch or folder of photos at once with Photoshop Elements Process Multiple Files tool, under the File menu.
I do know how to do that, but when you are picking photos out of a large group in the catalogue how do you do it, and then do the default setting in pe7 not sownsize the photos when you bring in and use to make a slide show?
When doing similar in Bridge (more or less the Organizer for PS and PrPro), I create a folder, and name it [Project Name]_Originals. I Copy these over to that folder, leaving the real "originals" where they were on my system. I create a sub-folder called "Resized." In PS, or PSE, I use an Action that I have created for re-sizing. I have several of these for different Project Presets. I go to File>Automate>Batch (will be different in PSE) and point to my [Project Name]_Originals folder as the Source, and my Resized sub-folder as the Destination. I check my settings and hit OK. In seconds hundreds of images can be resized to fit the Project. Then, I Import (Get Media Files & Folders) and navigate to the Resized sub-folder.
Note that there are slight differences in the syntax between Photoshop and PSElements. There could also be slight differences between Organizer/Albums and Bridge. As I use PS and Bridge, my instructions are for those two specific programs.