right well the first post suggested some1 was using another computer with your IP address,
the last post suggested some1 was hacking your computer ? which is it.
the chances is if your with virgin broadband then you have a dynamic ip address which mean your probably wont have the same IP for longer than 3 weeks at a time.
for example i just put my ip address in this website http://www.ip-adress.com/
which is ment to be an IP tracer (tells you the location of ip) and it says im in leeds when im actually in milton keynes.
which means the last time this ip was registered with that website it was in leeds or my nearvest server is in leads.
basicly your IP address will constantly change therefor any1 trying to "imposter" your IP was probably doing it by accident