I've done all of my covers using Word.
Frankly, it's the only way I know how and yes, it was a struggle to figure out. But my covers are very simple in design. (You can click the link in my signature line to see my few covers if you like. they were all done with Word.)
When I published my first book, I thought Lulu's little cover wizard made horribly generic looking books with few options for creativity and after the initial go at it, never looked at it again. That was 5 years ago. A single-piece PDF just seemed easier and better to me.
A Quick Procedure:
1. Start with a blank document in landscape orientation and set paper size to what Lulu wants in the upload section.
2. Word seems to default to at least 0.1" margins on the custom size. Set these margins to 0.0" and click IGNORE when it tries to fix them. Setting paper color to white or black or whatever doesn't hurt.
3. Create a blank drawing canvas and Rt-click Size it to fully fill the blank paper size. When you want to place images, create a new drawing canvas for each, Insert Image into the drawing canvas, resize the image, and drag the sides of the canvas in to near the edges of the image. Then you can position the new canvas where you want. (Pre-make your layered JPG's with GIMP or what have you.)
4. For titles, use Insert, Wordart. This allows you to turn things sideways for spines and such. Use text boxes for back cover blurbs.
5. Select all elements and group if you like. This allows you to position all spine elements or front cover elements together.
6. Save As PDF using your PDF add-on utility. Be sure to save it as the same size as the document's paper size, and be sure to check the IMBED FONTS box.
7. Upload to Lulu and examine it with the cover pre-viewer. If it looks right, proceed. If it doesn't, adjust the features in your Word Doc, re-save as PDF, and upload again.
This may seem clumsy to the more experienced folks like Maggie and Ron, but considering my limited experience with graphic arts (zero) and tools on hand (Word and Paint and LView and GIMP), I'm happy with my results. (I'm not paid by the hour.)