By Aidan Malley

Published: 12:00 AM EST

An Illinois-based company and its Nevada partner have filed a lawsuit against Apple Inc., alleging that Mac OS X 10.4 "Tiger" treads on an interface patent that affects the operating system's nearly universal use of tabs.

Little-known intellectual property agency IP Innovation LLC and its parent Technology Licensing Corporation this week became the latest to claim that Apple had abused a patent they hold.

Filed April 18th in a US district court in Marshall, Texas -- a town frequently recognized as the preferred home for lawsuits by companies that hoard property claims -- the four-page formal complaint purports that Apple has engaged in "willful and deliberate" infringement of a computer control patent by selling its current Tiger operating system.

IP Innovation is demanding a jury trial and asks for reparations for perceived damages which "exceed $20 million," according to the suit. It also seeks an injunction that would prevent the California-based defendant from infringing on the patent, essentially blocking Apple from continuing to sell its current edition of Mac OS X and any future editions that might draw on the supposed infringements.

The reported violation is an exceptionally specific one. It refers to a single US Patent Office filing originally made by Xerox researchers for a "User Interface with Multiple Workspaces for Sharing Display System Objects" -- and, in turn, a lone claim within that patent.

The disputed section refers to the technique of creating a window on a computer's screen with controls that switch between views of multiple associated display objects within the window, erasing one view as the user selects another while still giving a spatial frame of reference and the same general interface during the switch.

While IP Innovation doesn't refer to any one feature of the Mac OS as copying the interface technique, the central claim may potentially apply to any of several approaches to navigating software used by Apple in Finder and its companion program. Category dividers triggered by Spotlight searches, as well as page tabs in the Safari web browser, bear the closest similarity to the now 20-year-old description.

Apple's Spaces virtual desktop feature set to arrive in Mac OS X Leopard would not be affected by the conditions of the immediate lawsuit.

Numerous questions remain unanswered in the legal motion and the associated patent, including subjects of prior art, ownership, and timing. Originally filed in 1987, the patent was last updated in December of 1991 with Xerox as the lone corporate owner -- nearly 14 years before the allegedly infringing software was released. The plaintiff in the new case has also chosen to make its case almost exactly two years after Tiger's April 2005 introduction and just months before the projected October release of Leopard, which should phase Tiger out of the market.

Regardless of the individual merits of the case, Apple has so far chosen to remain silent on the matter after having received notice of the impending court case earlier this week.