You shouldn't have to convert the images. Poser 4 on the mac reads jpg's perfectly fine. The conversion you read about probably refers to bump maps. They are usually distributed as jpg's instead of bum-files because the bum-files are huge and Poser will convert them for you. To convert do like this: open Poser. Don't load your character yet, but instead load a simple prop. The box will do fine. Open the material editor and in the bottom left corner you will see an option to load bump maps. Click on the button to navigate to the folder where you stored them. If you didn't turn off the option you'll even see a miniature version of the jpg. Load it and Poser will ask you if it should convert it for you. Let it do that. Repeat until you converted all. Unfortunately I can't show you a picture as I only have Poser 5 on my computer now. Hope this helps you.