Most of the time, Windows 2003 and XP behave correctly when communicating with a Windows 2008 Read Only Domain Controller. RODCs are extremely handy for branch offices, especially when combined with Bitlocker, for extra security for remote locations.
This update, KB
944043 helps work around some of the known issues that 2003 and XP do not know how to handle out of the box, because RODCs did not exist when they were originally programmed.
In general, you'll want to deploy this on your network before you deploy any RODCs to prevent any of these potential "gotchas". So far, it has been my experience that "everything just works" with RODCs without these updates, but I don't have some of the exotic setups that these known issues arise from.
