The writer claims that Apple is reviving "Yellow Box for Windows" -- a development environment which promised Mac OS X developers the ability to develop and then deploy on both Mac OS X and Windows environments. The original plans for Yellow Box were promised during early developer sessions by Apple, but later killed.
The letter claims that the project has been relaunched internally under the name "Dharma". Resultant applications will be true "Universal Binaries", allowing developers to release their applications under the Windows environment also.
The reasoning behind this is the same as it was before -- lure developers (Mac and Windows alike) to the Mac OS X platform to stimulate more Mac applications and compatibility. Safari is reportedly already running on Windows XP and is expected to be released as a free application for Windows.
Obviously, anonymous forum posts are amongst the least reliable sources of information, but is linked here for interest sake.