I don't follow why you want to run a 12 year old OS, which is now at EOL status, meaning there will be no future security fixes past the one-off Microsoft just made, just so you can run some equally outdated AV software that will apparently not work with any later versions of Windows? So how exactly is this a good idea again?
If you had some legacy piece of specialty hardware or some poorly written, but sadly vital, program which would not play nicely with the API rule enforcements that started getting teeth with Vista... Maybe. I can also understand not wanting to try and run any newer OS on such an old CPU, which is why I suggested Linux. It runs quite well on older hardware, there's less need for a comprehensive AV suite like on Windows... Linux isn't a carte blanche check to do any stupid thing you want on the Internet, but you're afforded a little more of a safety net than Windows.
Since I haven't seen mention of either of these things anywhere in this thread, I'm left wondering why you would intentionally want to leave yourself open to who knows what, with the full knowledge that it will never be fixed.