Can these open source patches be applied to actual XP or do you have to be running a private version?
Not certain what you mean in your question. My experience has been that when a vulnerability was discovered then the ‘nix community spread the word and then pitched in to develop a fix for it, testing it against all versions and posting which patch worked in which OS. They always tried to develop a single patch that worked across all variations but even if not possible then the various patches were posted on numerous sites with appropriate notes as to which one(s) worked on which versions.
Many times the Redmond crowd disliked admitting that there was even a problem at times, and either quietly included it in their next Security Update or simply pointed people to the already-posted fixes.