Apple won a key victory in its legal battle with Psystar, as a federal judge has ruled that the clone-maker violated Apple’s copyright when it sold PCs with Mac OS X pre-installed.

“Psystar has violated Apple’s exclusive reproduction right, distribution right, and right to create derivative works,” U.S. District Judge William Alsup wrote in a ruling released late Friday. (Get a PDF of the judge’s ruling at Groklaw.) “Accordingly, Apple’s motion for summary judgment on copyright infringement must be granted.”

Alsup’s ruling affirms Apple’s argument that the end-user license agreement for Mac OS X restricts the use of the operating system to Apple-built computers and specifically prohibits customers from installing the OS on other PCs. Similarly, the judge rejected Psystar’s argument that the first-sale doctrine allowed it, as a buyer of OS X, to do with the operating system as it pleased.

Additionally, Alsup granted Apple’s claim that Psystar violated the anti-circumvention and anti-trafficking provisions of the Digital Millennium Copyright Act. The judge rejected Psystar’s argument that Apple was misusing its copyright.

Alsup’s ruling came a month after both Apple and Psystar had filed for summary judgments in the case. The maneuver is a common one in legal circles, in which the parties ask the judge to decide the merit of a case before trial based on the arguments both sides have filed.

Alsup’s ruling did not cover several other claims filed by Apple involving breach of contract, trademark infringement, and other issues. The judge’s ruling also did not address any relief Apple may be entitled, too. Previously, the computer maker had asked for a permanent injunction that would bar Psystar from selling any more hardware with Apple software and force the clone-maker to recall every OS X machine that it’s sold.

While Friday’s ruling was a definitive victory for Apple, it may not be the end of the company’s legal contretemps with the Miami-based clone maker. In August, Psystar filed suit against Apple in Florida, claiming that Apple illegally ties Snow Leopard to its hardware. Psystar has been selling Mac clones with OS X 10.6 installed.

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