IM spamming?

Yesterday morning I received a request for an add to Yahoo IM. The name looked familiar and I figured it was one of my buddies who changed accounts. My account name is pretty unique and not something someone would just guess at. Last night I got nailed with dozens of IMs at once and it shut yahoo down. It happened 2 more times. I have found out who the guy is that did this. Is there a way for me to trace the IP address the spam IMs were coming from? I have disallowed IM's from anyone not in my list and of course removed that account from my list. I've run AV and checked for malware and I'm clean. I'd like to throw a curve ball back at this duffus. Anyone got some ideas for me?