It's hard to prove such a thing as multiple accounts.
Ip numbers can be identical due to modem dial-up connections.
Hovewer: on the PBW I'd avoid playing with the following players:
Ghouls
Blacky
Dark ATM
Winter
Mao Dzedun
Joker
Alex Reaper
Stalin
Why? Check this:
http://www.shrapnelgames.com/cgi-bin...;f=23;t=008475
Nothing can be proved but I know I won't play with them again.