You should be fine as long as your not sharing, and your running win2k.. if your running win9x, im sorry. what they do is they scan you, and they stick your ip in there "LMhosts.sam" file. in this case when the computer is started up, it will pretend that your on his lan. as long as you got passwords, and you got nothing sharing you should be fine. if you do, turn off NETBIOS/NETBEUI, and to network your computers just use the TCP/IP trick 192.168.0.X. (Interal Routing) Personally, i hate NetX just because at times it can be very vulnerable. Hope this Helps.

Oh one more thing, Check your ISP, which ISP are you using? because if your using a Well Targerted ISP, they can continue Guessing the IP, ont the top of that, check your IP everytime your dial on. It may be that your ISP is dishing you out the same ip. If thats the case go to the command prompt and type "ipconfig /renew" and get a new ip. just keep on it. then after your done with that and you still feel iffy, go grab some software related firewall, and make sure you dont open anything from anywhere.