Also, be mindful of the overall file size of the images. A .psd or .tiff file will usually be much larger than a comparable .jpg with the same pixel dimensions. Premiere Pro & Premiere Elements are very sensitive to the overall load caused by multiple images. I have the scar tissue to prove it.
I suggest you find the smallest jpg sizing that will still look good when displayed in your final project (DVD, online gallery, etc.) and run a few tests as you increase the number of images. And save your work often to guard against system crashes.
Let us know how it goes. Working with still images doesn’t get enough reference/support in the Premiere world…it’s often glossed over in instruction books and online help.
– Mike –