all an IP address is a address for your computer to access the outside world...sort of.
Behind EVERY WWW address there is a IP address. and obtaining this address can take 3 seconds. So this person cant do anything with your IP except ping you to death (lol)
In order for him to do all those things, he must have hacked your machine and/or accounts.
I would check for Trojans on your computer. Use adaware, and a virus scanner, norton, mcfee, etc.
Common Trojan programs are sub7 and BO2k.
BO2k being the strongest IMO.
Just change your passwords, and your IP address.