Start here, if the file you downloaded is the real Jaguar disk1, it is not an upgrade. Jaguar is a two disk set and you need both disks for installation. Many of the Jaguar.dmg like any of the files on gnutella networks are not the real thing. Or they have been corrupted or just started bad to begin with. But let's say it is real and good. You need to have os10.1 to os10.5 to open a dmg file. OS9 does not open dmg files. The disk copy for os9 opens and writes .img files, os10 does .dmg files. Maybe Toast 5.1 or 5.2 might be able to open it in either os. It does in 10. That's something to check at the roxio web site. And finally, Yes you would have to burn it to install it. Then again you should just buy it and save the trouble. OS 10.2 works great, I bought it a month before it was released. Can't remember the last time I started os9. Guess I just don't need it anymore.