Having booted and used 10.5.6 on 128MB, I would say it was more than slow, in fact Ive seen glaciers that moved faster than it. (This was on a 700Mhz G4 eMac and installed by target disk mode to see if it would boot - It does, but if you open any application, at all, or even move the mouse, it lags) - However give it 1GB RAM and it runs beautifully (I have it on my 450Mhz G4 with 1GB RAM, and with the graphical things turned off, it runs perfectly), and its an upgrade thats easily worth it for $40 or less.