"threatened" is kinda ambigious.... how exactly?
Also, knowing someone's ip address isn't too difficult, however, it is illegal to knowingly break into someone's wireless network, with intention to cause malice. granted its pretty easy to do if you know how, but then, so is picking a lock. Are you in a network in the first place?
If you are networked wirelessly especially, the onus is on you to report any suspicious activity. It might help abit to change passwords, etc, but really, its a lost cause if someone is serious about hacking in.