Longtime US computer software rivals Microsoft and Novell unveiled an alliance today to make their competing programs interoperable. The alliance was devoted to "building a bridge" between Microsoft's patent-protected software and Novell programs based on the free, open-source Linux operating system, according to the companies. "A number of people said it couldn't be done, but we think we found a solution that respects both business models going forward," Microsoft chief executive said at a press conference in San Francisco.