i made a server and only i was on it and he came on and we talked

Could have been for several reasons. If it was a server that was using craftbukkit it was more than likely the were using the plugins MobDisguise which can allow you to change to any player and adopt their minecraft skin.

You say that you were "on a server" and you say "I believe Notch was on MY server" so which was it?
if it's your server check for minecraft/world/users/Notch.dat

Also don't capitalize every word you write.. it's weird..

Notch realy where on my server because he helped me build then he left after that

sorry i wont do it next time

I used to trick people all the time on servers. I used to have cracked minecraft and I changed my name to notch and started playing on servers as him. I had his skin too! I could change my name to whatever I wanted too and didn't need a password. Once, I changed my name to someone's that was playing on a server. I joined that server and it logged him out. I was playing as him! I had all his stuff! I could even play as and op or the server owner ( but I didn't want to get banned )