To run Basilisk II, you need a ROM image, which is a data file containing a copy of the ROM chips from a real 68k Macintosh.
The best way (i.e. most legally acceptable) to get a ROM image is to produce it from your old Mac. Take a program like CopyROM, download it onto your old Mac, and use it to produce the image file, which you then copy or upload to your OS X Mac. A good page which describes this process is here.
The easiest way to get a ROM image is to get one from someone else (e.g. another Basilisk II user, or an emulation web site). Note that this probably contravenes several copyright laws.
Once you have your ROM image, you need to tell Basilisk II to use it:
If you want to test this, press the Run or Power button (in the top right corner of the 'BasiliskII Emulator' window). After a few moments you should see a Mac screen, with a picture of a floppy disk with a flashing question mark. That is the Mac telling you that it needs a disk to boot from.
Basilisk II needs a copy of the MacOS to boot from. Anything from System 7
through to MacOS 8.1 should be usable.
(Felix Eng and I have only tested System 7.0.1, 7.1, 7.5.3 and 7.6,
although Felix also got System 6.0.8 to work with SE/30 Roms)
It is possible to use Basilisk II with a CD-ROM or floppy image, but because most bootable CDs have a minimal System Folder, it is better if you use a disk image with a more complete MacOS installed on it. The next section tells you how to do this.
Note that there is currently no Install CD image on Apple's Web site, but
they do seem to have MacOS 7.5.3 floppy disk images (all 19 of them). Burning
those images onto a CD (not in the extended format) should allow you to install
Thanks to Attilio Farina for this tip!
Before you can install the MacOS onto a disk volume, you need to create a disk to install onto:
If you want to have more than one hard disk available to Basilisk II, you could create additional volumes here.
Insert your MacOS install CD-ROM, and wait a few moments for the OS X Finder to mount the disk. While still in your preferences:
After the installer finishes it may try to reboot (or you may need to force a reboot). When it reboots, BasiliskII may exit. Start it again, and you should boot into your installed OS.
If Basilisk II is running MacOS 7.5.3 or newer, you can easily access some of the files from your OS X disks. Just set the 'Unix directory to mount' in the Volumes tab of the Preferences. Next time the Emulator starts up, a new disk will appear on its Desktop (called Unix).
To prevent clashes with the OS X desktop files, I suggest that the directory you select is not a whole disk (e.g. '/' or '/Volumes/disk'). Mount a sub-folder instead (like '/Applications (Mac OS 9)').
If you are not running MacOS 7.5.3 or newer, the above trick won't work. This makes getting files into Basilisk II harder. Luckily, older versions of Apple's "Disk Copy" utility can create a disk image file that is compatible with Basilisk II (i.e. you can add it as a disk volume).
Open 10.1's Disk Copy program, and create a "Mac Standard" image, or use Disk Copy 6.??? in Classic.