This latest version requires a RiscPC with at least 12MB free to run, and the screen memory needs to be cached for best playability (AutoVCache is available for just that). The older version is also available so that one can play it on older machines, but this still has some notorious bugs in it that have been fixed in the latest version.
Iain asks that if you like Spheres of Chaos, you should register it. The recommended price is £15.00 UK / $15 US, but if you can't afford that then pay what you can. Bearing in mind that you could afford the computer to play the game on, and Iain is in much need of money to pay for various essentials, such as food and rent (hint hint!). Spheres of chaos is available from http://www.chaotica.u-net.com/.