It stopped before completion with the following error:-
“ Setup failed while installing sub-component Exchange ActiveSync with error code 0xC0070643 (please consult the installation logs for a detailed description). You may cancel the installation or try the failed setup again”.
I found the solution here, http://geekswithblogs.net/colinbo/archive/2006/01/27/67345.aspx
To cut a long story short, replace the version of MSXML3.msi in your C:\Program Files\Exchsrvr\bin directory with the latest version and retry the operation.
I found a suitable version here, http://download.cnet.com/Microsoft-XML-Parser-MSXML-3-0-Service-Pack-7-SP7/3000-7241_4-10731613.html?tag=contentMain;overviewHead,.
Don’t worry if MSXML4 and/or MSXML6 are already installed. For compatibility purposes all versions can co-exist on the same server.