Have you tried any of the many Puppy linux versions? They are between 70 and 400 megs, with packages aimed at
various niches, office, graphics, music, comms etc, all built for speed on ancient computers. Fast even as live CD.
Check what the users say here:http://www.murga-linux.com/puppy/
Minime 2009 is excellent. As is RocXshoP . Both are small and fast, I use kde 3.5.10,
and only apps I really really need.