Following last week's delay, Microsoft finally releases Windows XP SP3 to Windows Update and Microsoft Download Center.
As to the issues last week relating to Microsoft Dynamics RMS, here's what a Microsoft spokesperson had to say:
Following last week’s discovery of a compatibility issue between both Windows XP SP3 and Windows Vista SP1 and Microsoft Dynamics RMS, Microsoft created and deployed a filter on Windows Update that will not offer either service packs to Microsoft Dynamics RMS customers. A fix for this issue is currently in testing at Microsoft and with customers and we hope to make it publicly available this month. Until then, Microsoft is advising Microsoft Dynamics RMS customers to not install either service pack. Microsoft Dynamics RMS customers running Windows XP SP3 or Windows Vista SP1 should contact Microsoft Customer Support Services for additional information.
Note: Microsoft Dynamics RMS customers should download and install this hotfix before applying Windows XP SP3 or Windows Vista SP1.