This post discussed about a problem with SFU 3.5 Interix and Password Synchronization components which break when you install Windows Server 2003 Service Pack 2. It also lists steps to fix it manually using files from another hot fix.
Microsoft has released a new hot fix - KB936529 - which fixes this issue and removes the burden of replacing the correct files manually.
If you've installed Windows Server 2003 Service Pack 2 and running in to this problem, please get this hot fix from PSS and install it. Make sure you don't install this hot fix on an R2 system because that may break correponding R2 components.