The standard PC peripherals will still work, and although you can only use one core, it's one core of a very fast CPU (relative to what was around when it was released and designed to run acceptably on), and gives you an idea how much "modern bloat" there is.
Well, ignoring the fact that WLAN/Ethernet won’t work without drivers (since internet is a bad idea with XP anyway), Sound and graphics don’t work either. So games are out, which is really the only reason I have for running XP. It’s too limited without working drivers and can’t be considered a working system.