Neowin.net have the latest Info about what's new in Windows 2000 SP3 RC build 3.140! here's a byte from their Article.
Some changes include Windows Installer (msi) was updated from 1.3 (SP2 level) to 2.0 rendering some installers completely useless (Trend Micro™ PC-cillin 2000 are affected)
Others are a direct response to Security concerns and implementation of fixes ASAP with the addition of Automatic Updates to the Control Panel of Windows 2000. This feature was limited to Windows Millennium & Windows XP respectively but has now found its way into Windows 2000 through SP3 making this as significant as SP3 was to Windows NT 4.0 in its day.
http://www.neowin.net