Microsoft is accusing rival IBM of orchestrating a campaign to block efforts to standardize Office document formats. <A HREF="http://news.zdnet.com/2100-3513_22-6159305.html?tag=nl.r23660">In an open letter released Wednesday,</A> Microsoft executives contend that IBM is trying to influence the standards process to limit choice. It also said that IBM is encouraging governments to mandate a document format that IBM favors.