Basilisk II emulates up to a 68040 Macintosh. You can install up to Mac OS 8.1 in the emulated machine.
There are two ways to get started with the emulator - installing MacOS 8.1, or System 7.5.3. This guide begins by describing how to get started with MacOS 8.1, which is a much faster and easier way to get started. Scroll down for instructions for System 7.5.3.