KB899158 - http://support.microsoft.com/?id=899158 

This article has had its ttitle changed from "MOM 2005 OnePoint database increases and Reports are empty or incomplete in MOM 2005 Reporting" to "How to Troubleshoot DTS and Database Sizing issues in MOM 2005 Reporting" in an effort to make it easier to locate.

This article provides great details in solving most of the top issues reported to PSS regarding the failure of the DTS transfer and space issues within the SystemCenterReporting database.