If you're referring to the Startup Tab, and/or non-Microsoft Services,
nothing MUST be enabled there for Windows XP to run. But as mentioned, there
are a number of things that *should* run in order for apps and even hardware
to function properly, and if you're lazy like me and like things that
auto-update, there's always those things that do it for me.
When it comes to the rest of MSCONFIG, my policy is to leave that stuff
alone, period. But the fact is that you can disable everything on the
General tab under Selective Startup and *Windows* will run just fine. You
might not like the way it behaves, but it will run just fine.