Technically, you could make several different pictures folders and divide the photos into them. Then choose the option in System Prefs to change screen savers to change randomly every time. That may not be as specific as you want, but it may work for you.
I googled the slideshow you said you have and got one result with a bunch of junk on it. What do you mean you haven't found a Mac equivalent? Are you trying to get a program or a download?
-BMF
OS X allows you use the pictures in a particular folder as a screensaver. Sounds promising, eh?
The problem is that every time the screensaver starts it will begin at the very first picture in that folder. If you have several 1000s of pictures stored you will only ever get to see the first few hundreds.
Instead I want the screen saver to pick up wher it was interrupted AND to show the pictures in chronological order (randomize doesn't crack it for me).
On my PC I have a screensaver called fgphotoshow, but thus far I haven't been able to find a MAC equivalent.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic