my understanding is that using your IP they can trace it back to you, but if you have the computer connected to your wireless router than there is no way for them to know which computer or who exactly posted the message. this is because of NAT network address translation. they will however know that it came from somewhere in your home. i may or may not be correct on this.
can you please link me to whichever thread you are talking about or did you already delete it?