While playing on the yahoo pool game and, after I beat them, someone got started insulting me and then typed in my IP address. He then said he was a hacker and would be making my life "very difficult".

A. How did he get my IP address?
B. What damage can he do to my PC?
C. What can I do to prevent him doing anything?

I bought a pack with virus software and a firewall some time back but, although the pack said it was compatible with Win95, it wouldn't load on my PC. I loaded the virus software but couldn't be bothered to go and get a proper firewall.

His yahoo ID is mark197625 and he looks like a geek who has nothing better to do so I better take this seriously.

All help is appreciated.