The latest security update IS stable (as compared to the rest of Windows) it's just that the things that it does in the name of security might adversely effect programs that weren't designed with security in mind. I've been using it since it was released and haven had a single issue with any of my programs (your basic office suite with system admin tools).
Still - the XP's SP2 doesn't have the fix for this it's a standalone fix and suggest everyone download both.
http://www.microsoft.com/security/bulletins/200409_jpeg_tool.mspx