I'd suggest doing nothing at this point.
Two possibilities:
First, the hacker isn't actually at the address shown, he's working thru another infected/compromised computer.
Second, it's nothing more than a script kiddie scanning for PC's infected with sub7.
If it's just a scan for sub7, then he'll move on, since your PC isn't compromised, and continue searching elsewhere.
DON'T attempt to scan/ping back at them unless you know exactly what you are doing. If you try that you are doing two things, first you are showing that your PC is present (your firewall blocked/ignored the scan I assume) at it's a valid IP address, AND you run the risk of pissing somebody off which could in return bring you a denial of service attack or constant probing.
If you continue getting scanned/probed from that IP multiple times over a couple of days, gather up your logs and forward them to your ISP and his. If you are on cable/DSL ask your ISP to change your IP address, or force a change yourself if you can.
Good luck!
Duke