It's there for a reason. So people don't just sign up and Spam the market place with junk. Not saying you were going to do that, but I assure you without that rule it'd get filled up with crap rather quickly.
But since you are asking....I have a Celeron processor that came out of my grandmas computer that's like 5 years old. It's a Socket 370 processor and I believe it's only like 566MHz in speed....not a P4 obviously, but I have absolutely not use for it and getting a mobo for it shouldn't be too expensive. I saw this very chip on ebay actually lol
The only info on the chip says
566/128/66/1.5v and I believe the 66 is referring to the bus speed. Other signs on it are
that's all the info I got on it.