MBRICE Leopard seems to respond well to multi-processor systems. The key to remember is that Leopard benefits from decent amounts of RAM (768mb-1GB) and will also run quite a bit faster with a 32mb graphics card that supports Quartz Extreme at the very least. Turning off the 3D dock also helps performance.
It should run quite well on your Digital Audio 533, but it's not about to set the world of fire with its performance. If you need it to work at peak performance then Tiger 10.4 is still the champion, but if your main concern is running the very latest browsers or other software, then 10.5 should work well enough to handle thst.
(Version 2.3.2)