I have 10.5.8 installed on two 1.67ghz machines and they run with no problems. They came pre-loaded with Leopard, though, so I don't know what installing is like. One originally came with 10.5 and the other with 10.5.6 and I did have a few problems with automatic update where I had to download the standalone updaters to get them up to 10.5.8.