Before you can begin to create your games you first need to install Belle. In the downloads page
you can find packages for different operating systems. The package should contain all the necessary libraries, including Belle's engine.
In case there isn't one for your system, you'll have to compile the application from source yourself.
Belle works on many systems. Belle's editor is a desktop application that works on:
Belle's engine is different because it's a {web application} and that means it runs on your browser, either locally or over the web. So the underlying system is not much important for the engine, instead the browser is.
Belle uses the {Qt4} framework for the editor, which, among other things, makes it a lot easier to support various systems. If you installed Belle through one of the packages for your system you don't need to worry about installing this framework, since it comes already included.
{Qt4} is also very lightweight, so an application made with it can also be very lightweight and thus run well on most machines, even older ones. However, since Belle can load many different images at the same time and images tend to occupy a bit of memory (RAM), it's therefore important to have as much memory available as possible. The CPU can also be an important component, especially if working with many animated images.
Since the engine is a {web application} you'll also need a browser to run your games. Any browser that supports {HTML}/{CSS}/{Javascript} well enough will be fine, however modern browsers are recommended for a better experience. Here's a non-extensive list of supported browsers:
* Internet Explorer 7 and 8 don't support HTML5 audio, therefore any type of audio won't be available in these browsers. A fallback mode in Adobe Flash is being worked on.