Dave, Magento dynamically resizes images, no need to resize them yourself. You can use one image for multiple products by using the same filename. For example to use one image for two products and a second for the third, set the fields in the csv file like so:
product image small_image thumbnail
product1 /image1.jpg /image1.jpg /image1.jpg
product2 /image1.jpg /image1.jpg /image1.jpg
product3 /image2.jpg /image2.jpg /image2.jpg
Using the same image for ‘small_image’ and ‘thumbnail’ as the main image will make Magento dynamically resize it where needed. The image files go into media/import, and don’t forget the forward slash in front of the image name in the csv file.