Computer Alliance Expanded: Digital Equipment Corp. and Microsoft Corp. said they will expand their joint development and marketing of computers and advanced networking software for businesses. The arrangement is designed to help Digital's Alpha microprocessor and Microsoft's Windows NT operating software. Microsoft will lend Digital $65 million to help train 1,500 technicians in Windows NT. Digital already has 800 workers certified for Microsoft products. Microsoft will develop programs that can be run on computers powered by Digital's Alpha chip.