I was messing around with .Mac Slides Publisher (one of the lesser known features of .Mac), and I found some interesting hidden treasures. I had previously messed with Slides Publisher when it first came out, but I was disappointed at the lack of options for image compression (combined with the default setting of 'too much', in my opinion). I have recently found a way to replace the images uploaded via Slides Publisher with your own (arbitrarily compressed) images.
Use Slides Publisher to create a basic slide show of an image or two. This will create the directories and files needed to provide slideshows via .Mac. Now connect to your iDisk and look in the Pictures folder - you'll see a new folder called "Slide Shows," inside of which is a "Public" folder, inside of which are the images you uploaded with Slides Publisher. You'll also see an xml file called config.plist. The config.plist file looks a little something like this:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN"
"http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>BaseURL</key>
<string>http://homepage.mac.com/dre/.Pictures/Slide Shows/Public/</string>
<key>Images</key>
<array>
<string>Image-001.jpg</string>
<string>Image-002.jpg</string>
<string>Image-003.jpg</string>
</array>
<key>SizeOfSlideshowInBytes</key>
<integer>727771</integer>
</dict>
</plist>
You can upload your own images into the Pictures -> Slide Shows -> Public directory, and then either rename them to match the names in the Images array (that is, Image-001.jpg, etc), or else alter the array contents to match the names of your images. Also, update the SizeOfSlideshowInBytes to match the sum of the file sizes of your images (the numbers in parenthesis of each image file's Get Info window, or the 5th field of ls -l Terminal output). I'm not sure where or how this value is used, but it's there for a reason, I do declare!Mac OS X Hints
http://hints.macworld.com/article.php?story=2003040719345119