Set Windows Defender to automatic startup, and rebooted. It seems to theoretically be active at bootup, but it never showed a system tray icon. To get that, I had to manually open Defender... but it did actually start this time, rather than giving an error about the service.
As for the uxtheme patching, I honestly can't remember. I believe it was something automated, that was around back in 2007 or 2008, when I got this computer. I found it when researching prior to moving from XP to Vista, and had downloaded and saved it on my old laptop for transfer to this one, as I'd had no issues with the uxtheme patching of my XP laptop. Basically it was the first thing I did when I unboxed this laptop, and after I installed my desired theme, I never touched it again. I think it was a patcher specifically for Vista with SP1, but aside from that I don't remember. I could go try to find the old disc with the files on it, but I'm not overly hopeful it still exists.