WOW.....
The slowest HW that I've run OSX (starting with 10.0!) on is a 355 G3 iBook (indigo) with an ectra 128MB of RAM added to the 64 MB built in.
It was slower, but it served the functions that I needed it for:
1. browsing (DU & BB)
2. designing CD labels
3. converting MIDI files (made on Amiga!!) to MP3
4. Quake 1 and 2
5. a letter or two!
It worked.
And the speed was bareable. But then it just seemed so compared to my (at the time!) 68040 A1200!!
Before choosing an OS, think about your needs. If speed is the ONLY issue, stick with OS 9 or use this as an excuse to UPGRADE!!!
Yellowdog is universaly hated on the Mac front, but it installs and sets up easy! AND it has decent HW support. Go figure!