As far as wich is faster, you just need to look at the total size of all the images plus overhead. I prefer the javascript myself myself because the overhead is low and doesn't require downloading and installing any plugins (worst case would be if the client can't use javascript. Then the viewer would just see the first image only). Plus with the javascript slideshow you can optimize each image independently, and even use a mix of JPG, PNG, GIF if the file size is smaller. Often with real world images JPG is smaller (optimizing the compression level and striping the EXIF data), but with line drawings, cartoon like drawings, etc. PNG or GIF tend to be better.
Dialup has become almost unusable IMHO. It use to be you could turn off graphics and still get everything out of the website you needed, but it hasen't been that way for a while. Heck, replying to this message loads the editor (with all the buttons and smilies) and that takes 193k. The trips with kids page is just 331k, but with far fewer total files (ie. less overhead making connections which makes a difference with dialup).
The best thing you can do for dialup is make pages that are readable/usable without graphics turned on (better for search engines too I think). Just try turning off images in ie or foxfire and view some pages.
www.kohlikaliher.com,
http://slideshow.barelyfitz.com/ and even this forum are quite usable without images.
www.tripswithkidz.com on the other hand is a good example of what not to do. It's whole menu/navigation structure is a picture, and there doesn't appear to be any ALT text anywhere.
-Tim
www.honeyrunapiaries.com