OK, you've got a bunch of problems.
First, unless you anticipate having a huge number of products to keep organized (many hundreds of images), you are better off using the main /images/ directory for your base images. Only use the /dvd/ folder for images of dvds, and then only after you have mastered the basic image organization.
Second, your "small" or base product image should be named lavender.jpg. The additional image(s) should be named lavender01.jpg, lavender02.jpg, etc. These all go in /images/.
Third, your "medium" image (only one per product) should be named lavender_MED.jpg (underscore and capitals requred), and go in /images/medium/.
Your "large" images, which you don't appear to have tried to do yet, should be named lavender_LRG.jpg, lavender01_LRG.jpg, lavender02_LRG.jpg, etc., and go in /images/large/.