Yesterday, for a period of about 2 hours or so, some individual was using the "net send xxx.xxx.xxx.xxx(IP) " through command prompt yesterday, and sending me non-stop messages practically rendering ...

This is brought up repeately actually... First, use a firewall! If the system is XP, at least use the built in one. You can also disable the messenger service (set it to Manual) and reboot... But net ...