Droids don't do random reboots unless something is wrong. Generally it's an app that's causing the problem. Task killers and virus protection should not be used.
The idea that you have to root your phone and run a custom ROM to stop this is, well, outrageous. Custom ROM's for the most part have their own issues, I'll take a stock ROM any day over a custom ROM.
My recommendation is to remove any task killers of virus protection, do a Factory Data Reset, and run it with no added apps for a day or two. If you still experience resets then you have an issue with the phone. If not, start adding your apps back in a couple of time and see how it behaves. If reboots start again, you'll probably be able to narrow it down to the problem app.
Good luck.