Because of the license, you must use Mac OS X Server if you want to virtualize. If you get an early Intel Mac that will run 10.4, you can split the disk and install 10.4, 10.5, and 10.6 at the same time, although rebooting on each OS can be a problem.
There are more Mac OS X options for testing these days than just major releases of the OS. Depending on your target customers, you can also test on PPC, i386, and x86_64 architectures.
If you are fortunate enough to live near Cupertino, Beijing or Tokyo, and you are a member of ADC Select or Premiere, you can use ADC Compatibility Labs for this kind of testing.
Nevertheless, you could probably pick up a couple of old cars quite inexpensively and get a few varied equipment.
Joey hagedorn
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